[{"value":"AFE","id":"1","desc":"Authorization for Expenditure. The budget for an activity is normally approved as part of the work programme. However, not all companies allow the budget to be spent for that activity. Even though the budget is approved, prior to commencement of the activity, an Authorization for Expenditure shall be signed off by the management as final approval for spending the money allotted for that activity. AFE shall have higher accuracy of estimated expenditure than the budget."},{"value":"API","id":"2","desc":"see American Petroleum Institute."},{"value":"Abandonment of a Well","id":"3","desc":"After an exploration or appraisal well is drilled and evaluated, if the hydrocarbon presence is not encouraging, then the well will be abandoned permanently as per local regulations. Sometimes even a successful well is abandoned if re-entry at a later date and completion of the well for production is not planned. A producing well may be abandoned at the end of its life."},{"value":"Abandonment of a Field","id":"4","desc":"At the end of the life of a producing field, the field will be abandoned as per local regulations that may include transferring of all installations to the Government without any charges or decommissioning wells and installations and disposing the same as per local and environment regulations. Most of the operators set aside abandonment funds with plans in advance. More than onshore, abandonment costs of offshore fields are very expensive."},{"value":"Abnormal Pressure","id":"5","desc":"If the formation pressure is above the locally accepted normal pressure gradient then it is called Over Pressure or Abnormal Pressure. It is important to understand the possibility of over pressure or abnormal pressure in a well during the design stage so that well complications like borehole instability, kicks and blowouts can be mitigated or managed.\n\n"},{"value":"Absolute Density","id":"6","desc":"The Density of a solid or liquid substance at a specified temperature. "},{"value":"Absolute Permeability","id":"7","desc":"Permeability of a substance is its ability to flow through the pores of a rock formation. Absolute Permeability is the ability of a single fluid such as water, gas or oil, to flow through the pores of a rock formation that is totally filled with that fluid only. Note that the permeability of a rock formation filled with single fluid is different from that of a rock filled with two or more fluids"},{"value":"Absolute Porosity","id":"8","desc":"Porosity is a measure of pore spaces in a rock formation. It is normally expressed as a percentage of ?pore space? to the ?total bulk volume? of the rock."},{"value":"Absolute Pressure","id":"9","desc":"It is the total pressure exerted by a system and is equal to the sum of Gauge Pressure and Atmospheric Pressure"},{"value":"Absolute Viscosity","id":"10","desc":"It is the resistance to flow encountered when one layer of fluid attempts to move over another layer or plane (relative mobility). It is basically the resistance offered to shear and flow"},{"value":"Accelerator","id":"11","desc":"It is a cement additive (see additives) used to reduce or speed up the setting time of cement slurry thereby reducing excessive waiting times for the cement to set. 2. Accelerators are also used as jar accelerators to assist to increase impact of jars ? see Jars and Jar Accelerators."},{"value":"Acid","id":"12","desc":"Liquids that have pH value less than 7 are called acids."},{"value":"Acidity","id":"13","desc":"Liquids that have pH value less than 7 are called acids. The intensity or strength of the acid is represented by Acidity. A liquid of pH 7 is a strong acid and pH of 1 is a weak acid."},{"value":"Acidizing","id":"14","desc":"Acidizing is a stimulation treatment to reservoirs. Acid is injected at a pressure lower than the formation breakdown pressure to improve Productivity or Injectivity. It is generally used to improve the near wellbore permeability by removing the plugging formed during drilling, testing and\/or completion."},{"value":"Acoustic Log","id":"15","desc":"Acoustic logs use sound energy to measure certain aspects of the formation or the cement quality behind the casing. The most popular logs are (1) The Acoustic or Sonic Logs ? which are used to determine the porosity of the formation, (2) The Cement Bond Log (CBL) ? which is used to determine the cement bond quality behind the casing, carry out a Check Shot Survey and develop a Vertical Seismic Profile (VSP)."},{"value":"Acoustic or Sonic Logging","id":"16","desc":"It is used to determine the porosity of the formation. An Acoustic Log measures the time it takes for a sound wave to travel through a given distance of rock at a given depth. The speed of travel depends on the rock?s composition and the type of fluid(s) it contains. Due to this property, Acoustic Logging is useful for determining the porosity."},{"value":"Accumulator","id":"17","desc":"It is a part of the Well Control system on a rig. The Accumulator holds a large volume of hydraulic fluid stored under high pressure using nitrogen and delivers the hydraulic energy required to open and close the BOPs (see Blow Out Preventers) and the Remote Control Valves. It is an important and very critical equipment on a rig."},{"value":"Active Mud Tanks","id":"18","desc":"Mud tanks form a part of a rig?s circulation system. The mud is stored in the mud tanks. The active mud tanks hold the mud that is being circulated by the mud pumps into a well bore (the mud in those tanks is active)."},{"value":"Adapter Spool","id":"19","desc":"A Spool that is used between the Wellhead and the BOPs. The spool will match the connections and pressure ratings of the wellhead at the bottom and that of the BOP at the top."},{"value":"Additives","id":"20","desc":"They are mostly chemicals that are added to the drilling mud, cement slurry or brine to enhance or reduce certain properties or parameters of the system. For example, Viscosifiers are additives used to increase the viscosity of a mud system and Weighting Agents (like Barite) are chemicals that are used to increase the density of the mud."},{"value":"Adjustable Choke","id":"21","desc":"The Adjustable Choke has an adjustable orifice, which is used to regulate the flow of fluids and the pressure on the upstream side. This is highly useful in a well control situation to circulate and control a kick. The adjustable chokes can be manual or auto that is controlled by a remote controlled panel."},{"value":"Adjustable Kickoff Tool (AKO)","id":"22","desc":"It is a type of deflection device and forms a part of the downhole motor assembly. It is used to kick off or deflect the hole from vertical in a directional well. This is a field adjustable kick off sub as compared to a fixed bent sub or bent housing. This allows the deflection angle to be varied on the rig floor from 0 deg to 2 or 3 deg depending upon the size of the motor."},{"value":"Aerated Mud","id":"23","desc":"Air or Gas is injected into the drilling mud to reduce its density. An Aerated \/ Lighter drilling mud exerts lower pressure at the bottom thereby reducing the chip hold down effect and permits faster drilling by removing the cut rock chips immediately after they are cut by the bit so that the bit always cuts into fresh formation."},{"value":"Air Drilling","id":"24","desc":"Air Drilling is a method in which compressed air is used as the drilling fluid instead of conventional mud. Using compressed air increases the rate of penetration and it also removes the cuttings with equal or greater efficiency. However, when drilling through formations containing water, the ability of air to remove cuttings efficiently is reduced if water enters the system."},{"value":"Air Hoist","id":"25","desc":"A Pneumatic (operated by compressed air) Winch used to lift and lower objects like drill pipes, elevators, slips and other equipment. Normally the air hoists are installed on the rig floor, substructure, derrick and sometimes on the deck or end of the catwalk. "},{"value":"Air Weight","id":"26","desc":"The Weight of an Object in Air."},{"value":"Age of the Earth","id":"27","desc":"+\/- 4.6 Billion Years."},{"value":"Agitators","id":"28","desc":"A Motor-Driven Paddle used in mud tanks to agitate and hold the solids of the mud in suspension and to prevent settling of the solids in the tank. "},{"value":"Air Gap","id":"29","desc":"It is the distance between the bottom of the hull of a rig (at elevated condition) to the surface of the sea. "},{"value":"Altitude or Elevation","id":"30","desc":"It is the height of a location measured from mean sea level. It is very useful as most of the subsurface target depths are indicated as m TVD SS (meter true vertical depth subsea) and hence the correct altitude (or elevation) at the drilling location is essential to understand the depth as m TVD BRT (meter true vertical depth blow rotary table) or m MD BRT (meter measured depth below rotary table). As different rigs have different rotary table elevation from the ground level, this is important."},{"value":"Alluvial Fan","id":"31","desc":"A mass of sediment deposited by a flowing river at the mouth of a canyon formed at a point when the river flows from a mountain to plain. They are generally downward lobe shaped. The mass will be thickest at the point of origin and thins rapidly at the downstream side. The alluvial fans are composed of gravel and sand and may extend for kilometers. "},{"value":"American Petroleum Institute (API)","id":"32","desc":"An organization that standardized most of the oilfield drilling and producing equipment. It has publications, standards, recommended practices and bulletins. Most of the oil and gas companies follow API standards."},{"value":"Amplitude","id":"33","desc":"It is a signal reflected from the contact between two layers and its amplitude is related to the contrast between the acoustic impedance of each layer. The presence of gas sometimes creates significant amplitude anomalies. Studying such anomalies forms the basics for the exploration of hydrocarbons from seismic data. Sometimes the amplitude variations laterally may also be due to lateral facies changes. "},{"value":"Anemometer","id":"34","desc":"is an instrument used for measuring wind speed in the atmosphere.\n\n"},{"value":"Angle of Deviation","id":"35","desc":"It is the departure of the wellbore from the vertical. In the upstream oil and gas industry, the term is generally used to indicate the angle of deviation of the hole from the vertical. The amount of deviation is a function of the deviation angle, depth at which deviation started and the depth at which deviation (the horizontal distance from the vertical) is measured."},{"value":"Angle of Drift","id":"36","desc":"Also called angle of deviation. See deviation."},{"value":"Annular","id":"37","desc":"Refers to Details pertaining to the annulus."},{"value":"Annular Space","id":"38","desc":"Generally annular space is the space between two concentric circles. In the upstream oil and gas industry, it is referred as annulus meaning the space between say pipe and open hole or pipe and casing or between two casing"},{"value":"Annular BOP","id":"39","desc":"Annular Blow Out Preventer (it is also called spherical or bad type preventer) is the most versatile piece of equipment on the BOP stack since it can close around casings, drill pipe, drill collars, wireline, Kelly or even on open hole (although closing on open hole is not preferred as it may damage the rubber element). It has a rubber-packing element, which allows this flexibility"},{"value":"Annular Velocity","id":"40","desc":"It is the velocity with which the fluid travels in the annulus (i.e. between the drill string and hole or drill string and casing). The annular velocity is very critical as it is one of the variables in conjunction with other rheological properties for effective hole cleaning (that is to lift the cuttings effectively from the bit to surface). It is the speed of the fluid inside the annular space. It is one of the major variables in the process of clearing the drill cuttings from the wellbore. By maintaining the annular velocity at a certain speed in conjunction with the rheological properties of drilling fluid, the wellbore is kept clean of drill cuttings to prevent them from settling back down to bottom causing drilling related problems.\n"},{"value":"Anticline","id":"41","desc":"It is a fold system in the form of an inverted arc or trough. An Anticline is an important structural feature to develop traps of oil and gas accumulations."},{"value":"Anticline Trap","id":"42","desc":"An Anticline trap is a fold-type structure to trap hydrocarbons below the fold. "},{"value":"Apparent Viscosity","id":"43","desc":"It represents the total pressure required to cause a certain flow rate. It is a combination of both plastic viscosity and yield point (see the definitions). It is measured by an equipment termed as ?Rotational Viscometer?."},{"value":"Appraisal Well","id":"44","desc":"Appraisal wells are drilled after discovery of hydrocarbons in an Exploration venture to appraise the extent of the formations, confirm reservoir characteristics, the limit of the hydrocarbons, and to confirm commerciality of the discovery. The usual sequence in a field development is Exploration followed by Appraisal followed by the preparation of a Field Development Plan"},{"value":"Aquifer","id":"45","desc":"A saturated water bearing bed of strata in subsurface where water can move readily"},{"value":"Arbitration","id":"46","desc":" Arbitration is an important clause in a contract that is reserved for settlement of disputes after several unsuccessful attempts at reconciliation or to resolve amicably. Most of the countries in the world have arbitration laws. International arbitration is also considered, especially for agreements between countries and foreign investors."},{"value":"Arenaceous Rocks","id":"47","desc":"A group of detrital sedimentary rocks typically sandstones in which particles range from 1\/16 mm size to 2 mm size. The term sandstone is often used as a synonym for arenaceous rocks. Arenaceous rocks are accumulated either by wind action or water action. In case of water action, they form in fresh water, brackish, shallow marine and deep marine environments"},{"value":"Argillaceous Rocks","id":"48","desc":"A group of detrital sedimentary rocks typically clays, shales, mudstones, siltstones and marls. They may also contain colloidal material like quartz, carbonate dust, iron pyrites etc."},{"value":"Artesian Structure or Well","id":"49","desc":"A group of sedimentary rocks are tectonically altered in such a way that the water contained in the rocks is at an elevated level than the well that is drilled from a lower level. Due to the elevation, the water is at a higher pressure than normal for the area. So if a well is drilled through this high-pressure aquifer, the water gushes out as a fountain if not confined."},{"value":"Artificial Lift","id":"50","desc":"If the reservoir pressure becomes insufficient to compensate production pressure drawdown or if higher production rate is required, it is then necessary to install a suitable artificial system either by a pump (for example ESP ? Electrical submersible pump or SRP ? Sucker rod pump) or by injecting gas to lift the oil."},{"value":"Asphalt","id":"51","desc":"A naturally occurring hydrocarbon, which is very viscous in nature. They normally have high pour points thereby becoming solid at most of the room temperatures."},{"value":"Associated Gas","id":"52","desc":"Gas occurs in nature along with crude oil, either as free gas or as gas in solution."},{"value":"Atmospheric Pressure","id":"53","desc":"It is the pressure exerted by the atmosphere at the sea level. At sea level, it is approximately 14.7 phi (14.7 pounds per square inch) and is termed as one atmosphere."},{"value":"Attapulgite Clay","id":"54","desc":"They are two types of clay generally used. One is bentonite gel and the other is Attapulgite. Attapulgite is viscosity-building clay used generally in salt-water muds."},{"value":"Auto Driller or Automatic Driller","id":"55","desc":"Normally the driller releases the weight on bit manually by releasing the brake as required. Auto driller is a mechanism that allows application of the weight on bit at pre-determined set ranges that automatically control the weight on bit (WOB)."},{"value":"Axial Stress","id":"56","desc":"It is the sum of vertical stress and horizontal stress components in the axial direction. In a vertical well, the axial stress is equal to the vertical stress as horizontal stress component is zero. In a horizontal well, the axial stress is the sum of all the horizontal stress components along the axis of the well. Pipe drag adds to the axial stress."},{"value":"Axial Strain","id":"57","desc":"The change in vertical length, which is under stress, is axial strain."},{"value":"Azimuth","id":"58","desc":"In directional drilling, the direction of the well bore is called azimuth and is measured in the horizontal plane clockwise from the north. Generally, North is assumed as 00, East as 900, South as 1800, West as 2700 and again North as 3600. So an azimuth of 450 means the well direction is in between North and East in the N-E direction, an azimuth of 300 means the well direction is between North and East but in the N-N-E direction"},{"value":"BHCT","id":"59","desc":"It is an abbreviation for Bottom Hole Circulating Temperature. It refers to the temperature of the drilling fluid at the bottom of the well during circulation. This temperature is lower than the bottom hole static temperature."},{"value":"BHP","id":"60","desc":"It is an abbreviation for Bottom Hole Pressure. See Bottom Hole Pressure."},{"value":"BHT","id":"61","desc":"It is an abbreviation for Bottom Hole Temperature. It is the temperature of the formation fluid at the given depth of the well."},{"value":"Back-Off","id":"62","desc":"To unscrew to open threads of one pipe from another"},{"value":"Backup Tongs","id":"63","desc":"As the final torque is applied to a drill pipe connection or when torque is applied to break a drill pipe connection with a make up or breakout tong, a back up tong is required to hold the bottom\/other drill pipe to prevent its rotation. This tong is called the backup tong. See also breakout tongs, makeup tongs."},{"value":"Back Pressure Valve","id":"64","desc":"It is also called check valve and as BPV. It is used to hold pressure from the well by a check valve arrangement that allows flow in only one direction. From the other direction, it is automatically closed to prevent any flow"},{"value":"Baffle Plate","id":"65","desc":"Baffle plate is placed normally on top of the bit on the pin shoulder or in the box shoulder of a drill collar or even in the tool joint of a drill pipe in the drill string. The primary purpose of the baffle plate is to centralize the deviation measurement tool that is dropped from the surface or run on a slick line without affecting or restricting the flow of drilling fluid through it."},{"value":"Ball Up","id":"66","desc":"When drilling through clay sections, the clay particles adhere or stick to the bit, drill collars and drill pipes. If the particles are sticking to the bit cones, then the bit cannot drill and it called a balled up bit. Balling up normally happens when drilled through sticky clays or clay formations with inadequate circulating pressure, improper drilling parameters especially weight on bit (WOB) and rotary RPM and improper type of bit. Using synthetic oil based or oil-based mud will remove balling up problems. Some times if the balled up bit cannot be cleared downhole, the bit has to be pulled out of hole for cleaning as drilling cannot continue with a balled up bit."},{"value":"Barge","id":"67","desc":"A flat-decked shallow draft vessel. It is usually towed by another boat, as it may not have self-propulsion. They are mainly used as supply and store vessel to support oil field operations offshore."},{"value":"Barite","id":"68","desc":" It is a mineral called barium sulphate and is the most commonly used weighting agent to increase the density of the mud. Its specific gravity is 4.2."},{"value":"Barometer","id":"69","desc":"An instrument used to measure the atmospheric pressure."},{"value":"Barrel","id":"70","desc":"The most commonly used measure of oil. One barrel is equivalent to 42 US Gallons or 5.615 cubic feet or 6.29 barrels make 1 cubic meter."},{"value":"Basalt","id":"71","desc":"A fine-grained sometimes, glassy black coloured basic igneous rock, which from after magma released into the surface cools and solidifies."},{"value":"Basement Rock","id":"72","desc":"The suite of mostly crystalline igneous and\/or metamorphic rocks usually related to pre-Cambrian period that underlies the sedimentary or the oldest rocks in a given area. Earlier it was thought that these rocks seldom contain petroleum. However, it was discovered that fractured basement rocks contains significant amount of oil and gas. About 5% of the producing fields around the world produce from basement reservoirs."},{"value":"Basic Sediments and Water (BS &W)","id":"73","desc":"This is a kind of foreign material in oil and requires being limited within a specified range. This includes free water, sediments, and emulsified or suspended water. A BS&W of less than 1% is a widely accepted limit."},{"value":"Basicity","id":"74","desc":"Liquids having a pH value above 7 until 14 are called base liquids. pH of water is 7 and that of acids is below 7. The intensity of basicity moves from pH of 7 to pH of 14 i.e. liquids with a pH of 8 is a weak base as compared to a liquid of pH 14 which is termed as a strong base."},{"value":"Basin","id":"75","desc":"A large depression in the earth?s crust in which sediments are accumulated to form thick layers of sedimentary rocks. It may be of structural or erosional origin."},{"value":"Bedding Plane","id":"76","desc":"It separates each successive layer of a stratified rock from the preceding layer. In shale?s the rock splits along planes that are bedding planes. Some sandstone bedding planes are marked by changes of color, grain size etc but no preferred splitting occurs."},{"value":"Bed Rock","id":"77","desc":"The general term used for sedimentary stratified rocks underlying other unconsolidated soil."},{"value":"Bell Nipple","id":"78","desc":"It is a large diameter pipe that is attached above the blow out preventer at the bottom and to the flow line at the top. The purpose is to allow the return mud from the well to be diverted through the flow line to the shale shakers. It also serves as a conduit for the bit or any string to run from the rig floor in to the BOPs, Wellhead and the Casings."},{"value":"Bent Housing","id":"79","desc":"It is a special housing as part of the positive displacement downhole mud motor and is used on steerable applications with a bend of 10 to 30 to facilitate directional drilling."},{"value":"Bent Sub","id":"80","desc":"It is a short collar type tool with a fixed bent used to deflect the downhole motor to drill a deviated well or to take a curved path provided there is no rotation of the drill string. The bent sub is always placed between the motor at the bottom and a drill collar on the top. The degree of curvature depends on the bent sub angle and the dimensions of the motor, bent sub and drill collar in relation to the hole diameter."},{"value":"Bentonite","id":"81","desc":"A mostly Montmorillonite-based colloidal clay that swells when it becomes wet. Due to its good gel forming and natural clay properties, it is a major component in water based drilling muds."},{"value":"Bingham Plastic","id":"82","desc":"The drilling mud is a non-Newtonian fluid due its thixotropic property. This requires an initial threshold shear stress to initiate a shear rate giving motion to the fluid that is at rest. Bingham plastic is one of the earliest models used to describe the viscous behavior of clay based drilling fluids."},{"value":"Biocide","id":"83","desc":"Biocides kill or inhibit the growth of microorganisms such as bacteria, molds, slimes and fungi. They are used in the mud to kill the bacteria and prevent early decomposition of organic chemicals used in the mud."},{"value":"Bio-Stratigraphy","id":"84","desc":"The study of rocks based on their fossil content for determining the distribution, environment of deposition and age."},{"value":"Bit","id":"85","desc":"The Bit is the primary and most important tool required in the drill string to drill a hole. It consists of a cutting element with advanced bearing design to last long rotating hours (not applicable for PDC bits) and circulation design to provide adequate hydraulics to drill efficiently. The cutting element has many types ? steel tooth, tungsten carbide buttons or inserts, industrial diamonds or polycrystalline diamond compacts (PDC). The bearings range from basic non-sealed bearings to advanced journal bearing systems. The bit has specially positioned nozzles and uses the hydraulic force thus generated to improve drilling efficiency. The Bit is attached to the bottom of the BHA (Bottom Hole Assembly) consisting of drill collars and stabilizers."},{"value":"Bitumen","id":"86","desc":"Naturally occurring hydrocarbon. It is a tar-like material. Its composition is not definite but it can vary from a thick liquid to a brittle solid."},{"value":"Bit Breaker","id":"87","desc":"When the drill bit is made up to the drill collar or a motor, the bit breaker is used to hold the bit such that the final torque can be applied to the connection between the drill collar and the bit."},{"value":"Bit Drift","id":"88","desc":"The tendency of the bit to move away from vertical due to various forces acting on it while drilling (Including the BHA design and the formation bedding angles)"},{"value":"Bit Gauge","id":"89","desc":"A circular ring used to determine the actual size of the bit and also to estimate the amount of wear to the diameter of the bit after use."},{"value":"Bit Pressure Drop","id":"90","desc":"A major percentage of the mud?s circulating pressure is lost across the bit nozzles. Unlike the other pressure losses across the surface pipes, drill strings and annulus, the bit pressure drop is not a frictional loss but actually due to acceleration forces. An effective hydraulics system needed to drill efficiently depends on appropriate pressure drop across the bit nozzles."},{"value":"Bit Hydraulic Horsepower","id":"91","desc":"It is a measure of the work required to push mud through the bit nozzles that is related to the removal of cuttings from below the bit."},{"value":"Bit Record","id":"92","desc":"It is a record of all the bits used in a well with details of bit size, type, make, nozzles, meterage drilled, hydraulics parameters used, type of formation drilled, condition of the used bit etc. It is an important collection of data for evaluating past performance and planning for future drilling operations."},{"value":"Blast Joint","id":"93","desc":"It is a short sub run as part of a completion string. It is made of high abrasion resistant material. It is used to withstand external erosion from high velocity flow from the perforations or entrained solids. It is normally positioned across the perforations so that the flow from perforations is directed against the blast joint."},{"value":"Blind Drilling","id":"94","desc":"During drilling, the mud that is being pumped from surface travels through the drill string, bit and rises up in the annulus to return to surface. The mud is then recycled and pumped back in to the system. Sometimes, due to downhole losses the mud will not return to surface. The mud will be lost continuously to an underground formation. Curing of losses may become very expensive or may not be feasible. If it is safe, drilling will continue blindly without mud returning to surface. Mud is a source of information of formations drilled as it brings the drilled cuttings to surface. Hence drilling without mud returns to surface is termed as Blind Drilling."},{"value":"Blind Ram","id":"95","desc":"It is used in a Pipe Ram BOP. When the closing pressure is applied, it closes the open hole (without any pipe). It cannot be used against any pipe in the hole but in the open hole its two rams seal against each other shutting off the open hole completely."},{"value":"Blow Out","id":"96","desc":"A Blowout is the uncontrolled flow of gas, oil or water from a reservoir to the surface. A Blowout is one of the worst incidents in the oil industry as it brings dire consequences ? loss of life, environmental damage, loss of property and a significant morale loss.\n"},{"value":"Blow Out Preventer (BOP)","id":"97","desc":"BOP is an abbreviation for Blow Out Preventer. It is the secondary control available at the rig to control a kick (kick is inflow of formation fluids into the wellbore. See kick). The primary control while drilling a well is the weight of the mud used. If the weight of the mud becomes lower than the pressure of the formation fluids, the primary control is lost thereby allowing entry of the formation fluids into the wellbore. If the fluids that entered the wellbore are not controlled and circulated out, it will become a blow out causing severe damage to the environment, property and loss of life. Hence a secondary control is essential to control the kick. BOPs are hence one of the most essential and critical equipment on a drilling rig. The BOPs are operated (opened and closed) by hydraulic fluid under pressure using accumulator (see accumulator). The BOPs are categorised into ram BOPs and Annular BOPs. For Annular BOP, see Annular BOP. The ram BOPs are designed specifically to close around a particular size of a drill pipe or a range of drill pipe but the range is limited. To close the well without pipe ram BOPs use blind rams. The blow out preventers come in various sizes and pressure ratings. Some of the most commonly used ram BOPs are 20.3\/4? 3,000 psi, 13.5\/8? 5,000 psi, 13.5\/8? 10,000 psi, 13.5\/8? 15,000 psi, 11? 5,000 psi, 11? 10,000 psi, 11? 15,000 psi, 7.1\/16? 5,000 psi, 7.1\/16? 10,000 psi etc."},{"value":"Boot Sub","id":"98","desc":"This is generally used just above the junk mill to collect the chips of junk milled by the junk mill. While milling, lot of chips of ground junk will be produced and the circulating mud cannot carry all of them to surface but lifts the chips to fall into the boot sub. It can also be run on top of the bit as routine process to collect small bits of junk that may affect the bit and the drilling rate."},{"value":"Borehole","id":"99","desc":"This is a hole made by drilling. A well drilled is called borehole."},{"value":"Bottom Hole Assembly BHA","id":"100","desc":"The bottom hole assembly or BHA consists of the string below the drill pipe in a drill string. It primary made of drill collars, stabilizers and the bit or it can be a complex combination of several drilling tools including directional drilling assembly, etc."},{"value":"Bottom Hole Pressure (BHP)","id":"101","desc":"The pressure at the bottom of a borehole. In a static condition, it is equal to the hydrostatic pressure of the wellbore fluid (normally mud or brine or water). If the well is shut-in through blow out preventers, if an additional pressure is applied at the surface, then it is equal to the hydrostatic pressure of the wellbore fluid plus the pressure applied at the surface. In a dynamic condition, when the wellbore fluid is being circulated, then it is equal to the hydrostatic pressure of the wellbore fluid plus the pressure required to overcome the friction to move the wellbore fluid from the bottom of the well to the surface up in the annulus. \\ Hydrostatic pressure = 0.052 x Density of fluid in ppg (pounds per gallon) x True Vertical Depth in feet\n\nStatic condition when surface pressure is zero, BHP = Hydrostatic pressure\n\nStatic condition when surface pressure applied = Hydrostatic pressure + Surface pressure\n\nDynamic condition (fluid is being circulated) = Hydrostatic pressure + Annular pressure losses\n "},{"value":"Box Threads","id":"102","desc":"The threads on the box end of the drill pipe. The box end is a female connection. See also tool joint."},{"value":"Braden Head Squeeze","id":"103","desc":"This technique is used to pump cement in to a hole in casing either to remedy a poor cement job or to repair a hole in the casing. The drill pipe is run to the depth where cement has to be pumped. Pre-determined volume of cement will be pumped and placed across the depth of interest. The BOP then will be closed (Braden Head refers to the casing head) so that the liquids cannot move up in the annulus. When the pumps are started again and pressure is applied, the cement enters through the hole in the casing. Once the requisite quantity of cement is pumped, the drill pipe is pulled out of hole while allowing the cement to set and harden."},{"value":"Break Circulation","id":"104","desc":"Whenever mud circulation is stopped for a sufficiently longer duration say for trip to change bit or wireline logging, it gels or thickens as mud is a thixotropic fluid and the intensity of the gelling depends on the gel strength properties of the mud. Due to this, an initial stress has to be applied to move the thickened or gelled up mud. Sometimes high pressures are required to break the gel and establish circulation. This is called breaking the circulation."},{"value":"Breakdown","id":"105","desc":"Normally referred to a failure of rig equipment or service company equipment thereby interrupting the ongoing operations. It also refers sometimes to breaking down the formation during a fracture or squeeze job."},{"value":"Breakout Cathead","id":"106","desc":"A device attached to the cat shaft of the drawworks in a rig that is used as a power source to pull the breakout tongs so that torque is applied for unscrewing drill pipe. Usually located opposite the driller?s side of the drawworks."},{"value":"Breakout Tongs","id":"107","desc":"Tongs that are used to start to unscrew one section of pipe from another section, especially drill pipe coming out of the hole."},{"value":"Bridge Plug","id":"108","desc":"It is a tool used to isolate a perforated zone below so that another zone above is perforated for testing or production or cemented. It is either run by drill pipe or by wireline."},{"value":"Brine","id":"109","desc":"Brines are saline liquids mostly used for testing and completion operations. They are preferred because they do not have suspended particles when weighed up. Normal mud when weighed has particles like barite in suspension but the brine will have the salts (that used for weighing up) in solution. The suspended solids in normal mud will settle down after if left in static condition for a long time. The brine will not precipitate the salt at the designed well conditions and will remain as liquid for a long time. Secondly the drilling mud has particles that are not degradable even with acid and hence can damage the reservoirs during testing and completion. Brine hence is preferred as it may not damage the reservoirs as a drilling mud does. Operation of annular pressure operated drill stem test tools is not affected if brine is used. Brines can be made of salts of sodium, calcium, bromide and formates."},{"value":"Buck Up","id":"110","desc":"To tighten up a threaded connection (such as two joints of drill pipe or casings)."},{"value":"Build Up","id":"111","desc":"It is a term used to represent building up the hole angle or inclination from zero to the desired angle as per the well plan. The built-up is more generally represented as a rate, i.e. x0 per 30 m."},{"value":"Bulk Density","id":"112","desc":"It is the density of the rock and the fluids present in the pores of that rock."},{"value":"Bullhead","id":"113","desc":"Bull heading is an action to push fluids in to a formation by applying pressure. It is done mainly to kill a well during a well kill operation (if normal killing operations fails to kill the well) or after a testing operation. Bull heading is risky but sometimes it may only be the solution if normal methods fail. It is especially useful if the formation fluids contain toxic gases like hydrogen sulfide to prevent it from reaching the surface."},{"value":"Bumper Sub","id":"114","desc":"A fishing tool run as part of the fishing string. The bumper sub body moves up and down on a mandrel. It jars downward to give a downward impact on the fish to make it free."},{"value":"Buoyancy","id":"115","desc":"When an object is immersed in a liquid, the object experiences an apparent loss of weight due to the buoyant force of the liquid. The immersed portion of the object displaces a volume of liquid whose weight is equal to that of the object."},{"value":"Buoyant Effect","id":"116","desc":"See Buoyancy."},{"value":"Buoyant Weight","id":"117","desc":"The weight of the drill string in a well filled with the drilling fluid. The drilling fluid can be mud, brine, water or any other liquid. Due to the buoyancy effect of the liquid in the well, the weight of the drill string is less as compared to that in air."},{"value":"Burst Pressure","id":"118","desc":"The amount of internal pressure, or stress, required to burst a casing or drill pipe or tubing. Every pipe is designed to withstand a maximum burst pressure and when the internal pressure on the pipe exceeds the maximum designed burst pressure the pipe bursts."},{"value":"Burst Strength","id":"119","desc":"The maximum burst pressure a pipe or a pressure vessel can hold or withstand from bursting or being ruptured."},{"value":"Calcareous","id":"120","desc":"The term can be applied to a sediment or soil, which is formed from or contains mainly of calcium carbonate or calcite."},{"value":"Caliper log","id":"121","desc":"It is a wire line log used to measure the gauge of the hole drilled and to find areas of wash outs, caving?s, undue enlargement or others. Caliper log is very important especially to understand the annulus volume between the casing and open hole to estimate the volume of cement to be pumped."},{"value":"Cap rock","id":"122","desc":"It is an impermeable rock that is devoid of porosity and permeability that prevents the migration of oil or gas and traps them as a reservoir. Most impermeable rocks are clay, claystones and shales."},{"value":"Carboxymethyl cellulose","id":"123","desc":"It is one of the cellulose derivatives generally referred as CMC. It is mainly used in water based drilling fluids to reduce fluid loss and to increase viscosity. Their effectiveness is reduced as the salt concentration in the mud increases."},{"value":"Cased hole","id":"124","desc":"A hole in which casing has been run and cemented."},{"value":"Casing","id":"125","desc":"Casing is a steel pipe used in drilling to prevent the wall of the hole from caving in, to allow drilling of every next section safely, to protect the potable water from contamination (land operations), to prevent movement of formation fluids from one to another, to allow the reservoir sands to be cased safely such that the oil or gas can be produced to surface through completion tubing safely. The casing is run and cemented. The well will start from a big casing size and as the depth increases the size will be narrowed down at the reservoir depth. Casings come in various sizes but the most common are 30?, 20?, 18.5\/8?, 16?, 13.3\/8?, 9.5\/8?, 7?, 5.1\/2?, 4.1\/2? etc. Casings are supplied and specified in accordance with API 5CT standards and certain physical properties. Critical of them are : length (range 1 to 3), outside diameter, weight per unit length (usually pounds per feet ppf), grade (generally K-55, J-55, L-80, N-80, C-90, P-110, Q125 and V-150 ? based on minimum yield stress) and type of end connection (some API connections are BTC, LTC or STC and premium connections that are capable of gas tight seal ? many proprietary connections are available ? some of them are NSCC, NK3SB, Fox, New Vam, Vam Top, SLHC etc."},{"value":"Casing head","id":"126","desc":"See wellhead."},{"value":"Carbonate","id":"127","desc":"A type of sedimentary rock formed in-situ from the skeletal remains of marine animals or by the precipitation of carbonate material. General carbonate rocks are limestone or dolomite that consists mostly of calcium carbonate or magnesium carbonate."},{"value":"Catwalk","id":"128","desc":"It is a long platform usually 15 m to 18 m long with 18 inches to 36 inches height. It is made of steel and is located perpendicular to the V-Door of the rig. Cat walk is used to as a temporary staging area for drill pipes, casings or any other materials before being lifted to the rig floor by the air hoist or the crane. When the pipes or any other tools are laid down from the rig floor, it is used as a temporary staging area before being lifted by a crane to its storage area at the rig. May not be true ? but some story goes like this ?a person walking on this platform has to be as watchful as a cat as equipment can come from any direction on to this platform and hence the name cat walk?."},{"value":"Cathead","id":"129","desc":"Cathead is a spool connected to the draw works power. Its primary use is to provide power to tongs, chains, cables etc to apply torque or pull. It is operated by a clutch control at the driller?s console."},{"value":"Caustic soda","id":"130","desc":"Sodium hydroxide, NaOH is called caustic soda. It is used to maintain an alkaline pH in drilling mud. It is a very important chemical in mud products in the drilling industry."},{"value":"Caving","id":"131","desc":"Caving refers to well bore collapse causing several complications like hole wash outs, hole instability, mechanical sticking, poor cementing etc. Generally caving happens in shale\/clay sections. The mud design, properties and weight must be appropriate to ensure that the shale sections are managed properly. It is the first remedy available to stop cavings. It is also called sloughing."},{"value":"Cellar","id":"132","desc":"It is a pit in the ground usually constructed to an appropriate dimension to accommodate the wellheads such that the tubing head spool is in line with the ground. Although this policy may differ with some companies, generally the cellar accommodates the wellheads, mouse hole etc. It is also useful as drainage for water and other liquids that will be disposed subsequently."},{"value":"Cementing","id":"133","desc":"The art of pumping the cement slurry from the cementing unit to the well for primary cementing (to place the cement between open hole and casing) or for remedial cement jobs or for placing suspension or abandonment plugs."},{"value":"Cement additives","id":"134","desc":"Chemicals that are used with cement to make cement slurry to be pumped in to the well. The type and quantity of additives to be used is determined by the cement design and laboratory tests."},{"value":"Cement bond log","id":"135","desc":"The cement bond log is recorded to measure the quality of cement bon between the casing-cement and cement-formation. CBL-VDL (cement bond log ? variable density log) is the most common type of cement bond log. Advanced versions CET (cement evaluation tool), CAST and USIT (ultra sonic imaging tool) are also available."},{"value":"Cementation","id":"136","desc":"Cementation is the process by which the individual particles of sediment are held together."},{"value":"Cenozoic era","id":"137","desc":"The time period from 65 million years ago until the present. Within the Cenozoic era, in the tertiary period, rapid evolution of mammals and birds, flowering plants, grasses and shrubs happened. The quaternary to recent period saw the evolution of humans."},{"value":"Centipoise","id":"138","desc":"unit of viscosity."},{"value":"Centrifuge","id":"139","desc":"Centrifuges are a part of solids control system on a rig that is primarily used to remove fine solids from the mud and also for barite recovery."},{"value":"Chain tongs","id":"140","desc":"A hand tool consisting of a long handle and chain that that resembles the chain on a bicycle. In general, chain tongs are used for turning pipe or fittings where a pipe wrench cannot be used. The chain is looped and tightened around the pipe or fitting while the handle is used to turn the pipe to tighten or loosen it. Usually to hold the other section of the pipe moving, a back up chain tong is used."},{"value":"Chemicals","id":"141","desc":"In drilling industry, chemicals are generally referred to mud chemicals that are added to the mud to manage or sustain or modify certain properties of the mud like weight, viscosity, yield point, gel strength, fluid loss etc."},{"value":"Chip hold-down effect","id":"142","desc":"The holding of formation rock chips below the bit as a result of high over balance in the well bore (i.e., pressure in the wellbore is greater than pressure in the formation) thereby preventing the bit to cut fresh rock all the time. This reduces the rate of penetration of the bit. Removal of the rock chips as soon as they cut from its place is important and hence the mud system and the hydraulics must be designed to have a low chip hold down effect."},{"value":"Choke","id":"143","desc":"It is a device installed in a pipeline to manage the flow of fluids. It contains an orifice whose opening can be adjusted depending upon the requirement of the flow. It is installed after the X-Mas tree on the pipeline when used for production of oil and gas. In drilling it is used to control the flow of mud and well fluids and apply back pressure during a well kill operation."},{"value":"Choke manifold","id":"144","desc":"It is a manifold consisting of upstream and downstream valves. The upstream contains manual or auto chokes to regulate flow and to apply back pressure. In drilling it is used during the well kill operations and in testing it is used to regulate flow of oil and gas."},{"value":"Christmas Tree","id":"145","desc":"This is a critical component of completion string and production equipment. Christmas tree is also referred as X-Mas tree. It has a set of valves including a master valve and wing valve, a choke and connections and is installed on top of the tubing head spool of the wellhead (see wellhead) either directly or through a tubing bonnet. It provides a means to control the flow of oil or gas from the well, diverting them through the wing valve to the flow lines, ensuring safety of the facilities and also providing means for measurement tools and instruments an access to the well."},{"value":"Circulating density","id":"146","desc":"See equivalent circulating density."},{"value":"Circulating fluid","id":"147","desc":"See drilling mud."},{"value":"Circulating pressure","id":"148","desc":"The drill mud is circulated through a series of equipment and system. From the mud tanks it is pumped by the mud pumps through the standpipe manifold, rotary hose and swivel (top drive) to the drill string. It passes the bit at the bottom of the bit and rises up to surface through the annulus between the drill string and the hole. The energy required to overcome the friction encountered in the entire path (pumping the mud down in to the hole and allowing it to raise back up to the surface) is provided by the mud pumps and this is termed as circulating pressure. Pressure gauges are normally installed at the mud pumps, the standpipe manifold and at the driller?s console to adjust and monitor the circulating pressure. See circulating system for a schematic of the mud flow."},{"value":"Circulating rate","id":"149","desc":"The volume of mud pumped per minute is generally referred as circulating rate. It is measured as gallons per minute or barrels per minute or cubic meters per minute."},{"value":"Circulating system","id":"150","desc":"The circulating system is one of the most important systems on a rig. It consists of the mud tanks, mud pump, high pressure lines from mud pump to the rotary hose, rotary hose, swivel or top drive, drill string, bit and mud return line."},{"value":"Clastics","id":"151","desc":"Clastics rocks are sedimentary in nature and are formed by weathering, erosion and deposition of fragments of other rocks. Large pieces of fragments are called grains or clasts. Smaller pieces are called matrix. The grains and matrices are held together by a cementation. There are various types of clastic rocks and are formed based on the area and environment of deposition. For example, sand stones that are made of sand grains are formed in deltas, beach environment or desert sand dunes generally in high energy environment. Shale or clay or claystones are formed in swamp, lake or other low energy environment similar environment. Conglomerate made of gravel and sand form at the base of a stream."},{"value":"Clay","id":"152","desc":"A part of the detrital sedimentary rocks commonly clays, shales, mudstones, siltstones and marls. The clay grade is applicable for particles of size smaller than 1\/256 millimeter (4 microns) in size."},{"value":"Clay","id":"153","desc":"A part of the detrital sedimentary rocks commonly clays, shales, mudstones, siltstones and marls. The clay grade is applicable for particles of size smaller than 1\/256 millimeter (4 microns) in size."},{"value":"Clay based drilling mud","id":"154","desc":"They use water for the continuous phase and clay for viscosity and other parameters. Commercial clays used are generally bentonite and attapulgite. Other components for various properties are added as required. Clay based mud system can be non-inhibitive and inhibitive mud systems. Inhibitive mud systems are required to combat the hydrating and swelling of clays. Lime or gypsum based system are examples of inhibitive clay based mud systems."},{"value":"Coiled Tubing","id":"155","desc":"It consists of a continuous hollow metal pipe coiled up in a spool or reel. This can be run inside and pulled out of the well including a well under pressure. The system has its own power unit. Coiled tubing is useful in many ways ? to run inside a tubing to circulate a light weight fluid before perforation, activate a well by pumping light weight fluid, implement temporary gas lift, clean out the tubing that is filled with sand, salt, paraffin, hydrates etc, spot acid or solvents etc. Some times coiled tubing is also used to drill a well (slim hole only especially in reservoir section with an underbalanced system)."},{"value":"Collapse pressure","id":"156","desc":"Collapse pressure is the pressure applied from the outside of the pipe. When the collapse pressure is higher than the rated or designed collapse pressure of the pipe, then the pipe crushes or collapses."},{"value":"Collapse resistance or collapse strength","id":"157","desc":"The maximum collapse pressure a pipe can hold or withstand or resist from getting collapsed or crushed."},{"value":"Completion fluid","id":"158","desc":"A low solids mud or salt solution like brine used during well testing and completion of a well. It is selected to minimize the formation damage apart from having the ability to control formation pressure. Brine is especially more preferred than mud due to the ability of salt going in to solution rather than suspended solids that are present in the mud, which may settle after prolonged periods of time."},{"value":"Concurrent method:","id":"159","desc":"It is a method for killing the well after the primary control is lost and formation fluids entered the wellbore (called kick). In this method, the circulation of the mud will be started immediately after the shut-in pressures are obtained while at the same time the mud weight is increased simultaneously at a defined schedule to the required kill mud weight. It is also sometimes called circulate and weight method."},{"value":"Condensate","id":"160","desc":"A light hydrocarbon liquid with high API gravity that generally condenses out of gas. Its presence in the liquid form depends on the pressure and temperature at the reservoir. A condensate generally contains butane, propane, pentane and heavier fractions with little or no methane or ethane."},{"value":"Conductor pipe","id":"161","desc":"The conductor pipe or casing is the first casing that is run in a well. In general, it is run to cover all the loose unconsolidated formation near the surface so that further drilling can continue without problems, to provide the structural strength to install a blow out preventer system etc. In onshore (land operations), in addition, it is needed to protect the potable water zones from the drilling muds and well fluids. In offshore, it is mostly pile driven using a diesel or hydraulic hammer. In land operations, it is generally drilled, cased and cemented or sometimes pile driven."},{"value":"Coning","id":"162","desc":"Coning refers to reservoir water coning up in to oil or gas coning down to oil with changes to oil water contact or gas oil contact as a result of production. If the oil is pulled hard with high draw downs, coning will occur early. Coning is affected by the characteristics of the fluids involved and the ratio of horizontal to vertical permeability."},{"value":"Connate water","id":"163","desc":"Water retained or trapped inside the pore spaces or interstices of a rock during its formation."},{"value":"Connection","id":"164","desc":"In a general sense, connection is at the end of a pipe or fitting used to join it to another pipe or fitting or to a vessel. In the upstream oil and gas industry, it is generally used to indicate the action of adding a joint of drill pipe to the drill string when drilling progresses."},{"value":"Connection gas","id":"165","desc":"During drilling, mud is circulated. The annular pressure losses are transmitted as additional mud weight (see equivalent circulating density). However, when the circulation is stopped for a connection (see connection), the additional mud weight is temporarily lost until the circulation commences again. During this time, a relatively very small amount of gas may enter the wellbore. When the circulation commences again, this gas is circulated to surface and is recorded as connection gas. The connection gas is a critical component to identify the onset of high pressure zones."},{"value":"Contact","id":"166","desc":"A well defined boundary or surface of different fluids within the reservoir. Contact may be an oil-water contact and is defined as the boundary above, which oil occurs predominantly and below which water occurs predominantly. A gas-oil contact is defined as the boundary above which gas predominantly occurs and below which oil occurs predominantly. Similarly gas-water contact is defined as the boundary above, which gas predominantly occurs and below which water occurs predominantly."},{"value":"Continental crust","id":"167","desc":"The part of earth?s outer layer, varying in thickness from 10 kms to 75 kms that makes up the continents."},{"value":"Contour map","id":"168","desc":"It is a map indicating or showing lines connecting points of equal value ? say elevation or formation thickness etc. Examples are depth contour and time contour."},{"value":"Co-ordinates","id":"169","desc":"They are used to refer to a particular location at the earth?s surface. A co-ordinate consists of a combination of longitude and latitude numbers and Lambert co-ordinates of X and Y in meters."},{"value":"Core analysis","id":"170","desc":"It is to analyze the cores collected from a well to determine various parameters like porosity, permeability, lithology, fluid content, angle of dip, geological age, saturation, facies development, contacts and probable productivity of the formation. RCA (routine core analysis) and SCAL (special core analysis) are commonly used."},{"value":"Coring","id":"171","desc":"It is an art of cutting a core in its original condition from the well without disturbance so that the formation can be analyzed for various properties (see core analysis). Core heads and core barrels are specially run to cut the core."},{"value":"Corrosion inhibitor","id":"172","desc":"A chemical substance that minimizes or prevents corrosion in metallic equipment."},{"value":"Crooked hole country","id":"173","desc":"An area in which a particular subsurface formation makes it difficult to maintain the verticality of a hole."},{"value":"Crossover sub","id":"174","desc":"A short sub that allows different sizes and types of drill pipes to be joined. For example ? a sub that has 4.1\/2? IF connection on one side and 3.1\/2? IF connection on the other side is called a crossover sub that is used to connect drill pipes of 4.1\/2? IF and 3.1\/2? IF connections."},{"value":"Crown block","id":"175","desc":"It is part of the hoisting system on a rig. As the name suggests the crown block is installed at the top of the derrick or mast. It has sheaves mounted on it (the number of sheaves depends on the number of lines reeved and the rig design) in to which the drill line from the draw works is reeved and taken to the traveling block (which has equal number of sheaves as the crown block)."},{"value":"Crude oil","id":"176","desc":"They refer to the drilled formation fragments that are brought to the surface from the bottom of the bit in the hole to surface by the drilling mud. The cuttings are collected at the shale shakers, washed and dried for analysis by geologists to learn information about the formations drilled."},{"value":"Darcy","id":"177","desc":"A measurement of permeability. See permeability."},{"value":"DE flocculation","id":"178","desc":"The mechanism by which the solids that are stuck together (flocculated) are dispersed by either reducing the electrolyte concentration, raise the pH of the slurry and add thinners or dispersants to the system."},{"value":"Defoamer","id":"179","desc":"A chemical that minimises or prevents frothing or foaming in a (example cement slurry) mixture."},{"value":"Deepwater drilling","id":"180","desc":"A relative term used to refer offshore operations at water depths greater than 500 m. The reference point of 500 m keep changing and there is no clear definition for deep water. Some places it is considered as 1,500 m and deep."},{"value":"Degasser","id":"181","desc":"Degasser as the name suggests removes any gas from the drilling mud. There are two types of degassers. One is called poor boy degasser which separates the gas from mud at atmospheric pressure and the other one is called vacuum degasser which removes the gas at vacuum. Sometimes during a killing operations, both degassers are used in sequence the mud entering the poor boy degasser first where the lighter gas components are removed and then the mud enters the vacuum degasser where slightly heavier or the remaining gas are removed."},{"value":"Density","id":"182","desc":"It is defined as the mass or weight of a substance per unit volume. Its unit is generally kg\/m3 or pounds\/ft3 or pounds\/gallon (ppg)."},{"value":"Density log","id":"183","desc":"It is a nuclear log run on open hole principally to measure the specific gravity or bulk density of the formations. It is also called compensated density log (CDL) or litho-density log (LDL). It is held against the borehole to ensure close proximity to the formations. In operation, the source sends gamma rays to the formation which are absorbed depending upon the porosity of the formation and the remaining gamma rays are received by the detectors (normally 2 are used)."},{"value":"Depletion","id":"184","desc":"Depletion refers to the depletion of reserves of oil and gas in a reservoir or the depletion of the reservoir pressure resulting from production of the reservoir fluid. The intensity of depletion depends on the type of fluid, type of drive (see drive), draw down pressures and production rates."},{"value":"Depositional energy","id":"185","desc":"The energy of the depositional environment that characterizes a particular depositional environment. High energy environment carries away the finer sediments leaving behind coarse materials like pebbles and gravel. The low energy environment allows the settling of finer materials like sand to form sediments. As river flowing from a high to sea, it gradually passes through varying but successive lower environments."},{"value":"Depositional environment","id":"186","desc":"An environment in which at a set of physical and geological conditions sediments are deposited."},{"value":"Derrick","id":"187","desc":"Derrick (also called as mast) is the structure in pyramid shape above the rig floor where the crown block, monkey board, racking board etc are supported. The crown block is a set of pulleys through the to drill line (wire rope) passes to another set of pulleys in the traveling block which travels up and down in the derrick with or without the drill string. Derrick comes with different heights and capacities."},{"value":"Desander","id":"188","desc":"Desanders are hydroclones that are used to remove sand particles 50 to 70 microns. Hydroclones operate based on centrifugal force such that the mud with the smaller particles are returned to the active system while the larger particles are discarded. The usual size of desanders is 6? and above but the most common size is 10?."},{"value":"Desilter","id":"189","desc":"Like desanders, desilters are also hydroclones that operate based on centrifugal force but they remove still finer particles down to 20 microns or even less."},{"value":"Development well","id":"190","desc":"The development wells are drilled to develop the field and bring production in to stream. They are generally drilled after the exploration and appraisal wells are drilled and the field is appraised and a field development plan is approved. Developments wells can be vertical, deviated, horizontal, multi-laterals etc."},{"value":"Deviation","id":"191","desc":"It is the departure of the wellbore from the vertical. In the upstream oil and gas industry, the term is generally used to indicate the angle of deviation of the hole from the vertical. It is also referred to the horizontal distance the hole is deviated from the vertical (usually measured from the vertical at rotary table as the reference). The amount of deviation is a function of the deviation angle, depth at which deviation started and the depth at which deviation (the horizontal distance from the vertical) is measured."},{"value":"Deviation survey","id":"192","desc":"A survey taken to determine the deviation (angle from the vertical) of the well. There are two types of surveys ? one provides the angle and the other provides both the angle and direction."},{"value":"Digenesis","id":"193","desc":"Digenesis is a process in which sedimentary rocks undergo physical and chemical changes by compaction, cementation etc and by solution."},{"value":"Diamond bit","id":"194","desc":"Industrial diamonds is a hard material. These are imbedded in the cutting surface of PDC (polycrystalline diamond compact) or TSP (thermally stable polycrystalline) bits to drill hard and abrasive formations."},{"value":"Diapir","id":"195","desc":"An intrusion which forms a dome by rupturing the overlaying rock sometimes developing a narrow neck at bottom giving it a balloon like structure. Most common are salt domes. Igneous rocks can also form diapirs."},{"value":"Differential pressure","id":"196","desc":"The difference between pressures of two different fluid systems acting against each other. For example, the difference between the mud hydro-static pressure and the formation pressure at a particular depth is a differential pressure at that depth."},{"value":"Differential sticking","id":"197","desc":"If the pressure differential between the mud weight and the formation pressure is high, then drill collars of the drill string are pushed to one side of the well bore. If a permeable formation (like sand) with a good and thick nearly impermeable filter cake (formed by mud solids) exist across the area where the drill collars come in to contact due to the high differential pressure, then the pipe gets stuck to the wall of the well bore. This is called differential sticking."},{"value":"Dipmeter","id":"198","desc":"It is a log run to determine the direction and angle of the formation dip in relation to the borehole. It is also used to determine faults, unconformity and folds and locate fractures. This log is also used to evaluate the sedimentary textures in a rock."},{"value":"Directional drilling","id":"199","desc":"Directional drilling is a science of drilling a wellbore at a predetermined well trajectory, angle, and direction so as tointersect a subsurface target. Although wellbores are normally drilled vertically, it is sometimes necessary or advantageous to drill at an angle from the vertical. Some of the advantages of directional drilling are 1. Multiple wells from offshore structures and onshore locations 2. Drilling to subsurface target from inaccessible surface locations, 3. To circumvent a steeply inclined fault plane, 4. Drilling to a subsurface target avoiding a salt dome, 5. Drilling to a subsurface target in offshore from land, 6.Controlling vertical wells in crooked holes, 7.Relief wells to control a blow out, 8.Sidetraking and 9. Multi-lateral wells\n\n"},{"value":"Directional hole","id":"200","desc":"A wellbore intentionally drilled at an angle from the vertical as deviated well. See directional drilling."},{"value":"Displacement","id":"201","desc":"It is the horizontal distance from the vertical to a position of the bit at subsurface in a deviated hole. In vertical wells, the displacement is approximately zero. Another meaning of displacement refers to the act of removing one fluid (usually liquid) from a wellbore and replacing it with another fluid like displacing cement with mud or displacing mud with brine etc."},{"value":"Ditch magnet","id":"202","desc":"A powerful magnet placed on the flow line or near the shakers so that metal cuttings are removed from the return mud. The volume of metal cuttings is an indication of casing wear or very useful during milling operations to monitor the metal cuttings."},{"value":"Diverter","id":"203","desc":"Diverter is annular BOP (see annular BOP) used to divert the flow from the well instead of killing a well. When surface holes are drilled, the risk of shallow gas may exist. However, as the conductor casing shoe will not have adequate strength, in case of a shallow gas kick, the well cannot be killed safely using a BOP. Hence the shallow gas if encountered must be diverted safely away from the rig to prevent loss of life, damage to environment and property. For this the annular BOP is used as a diverter with a diverter lines and spool system."},{"value":"Dolomite","id":"204","desc":"A type of sedimentary rock rich in magnesium carbonate. It is a reservoir rock where petroleum can be found due to the development of secondary porosity."},{"value":"Dogleg","id":"205","desc":"The total curvature of the well bore (the combination of changes in inclination and direction) between two survey stations. In the drilling industry, the amount of dogleg is generally normalized to a standard interval usually 30 m or 100 feet."},{"value":"Dope","id":"206","desc":"It is a lubricant used on the threads of drill pipe, casing and tubing. The dope for drill pipes is different from that of casings. It is also called thread compound."},{"value":"Double","id":"207","desc":"singles of drill pipe or tubing joined together forms a double. See also single and thribble"},{"value":"Double board","id":"208","desc":"It is a working platform of the derrick man located on the mast of a rig to handle doubles (two singles of drill pipe or tubing). It is also called monkey board."},{"value":"Downhole motor","id":"209","desc":"This is also called mud motor and generally there are positive displacement motors and downhole turbine motors. The motors are powered by the drilling mud. They are attached to the bit and allows the rotation of the bit without the need for rotating the drill string above it. This is extensively used on directional drilling and performance (improved drilling rate) applications."},{"value":"Downtime","id":"210","desc":"Generally referred to the time during which rig operations are temporarily suspended because of repairs or maintenance."},{"value":"Drag","id":"211","desc":"Drag is a condition generally noted during connections or trips. Up drag happens when the string is pulled out of hole which increases the normal string weight. Down drag happens when the string is run in hole which reduces the normal string weight. Drag is a sign of hole is not stable or in condition. It may be due to various reasons ? sloughing shale, balled up bit and stabilisers or dog legs etc. "},{"value":"Drawworks","id":"212","desc":"The primary hoisting mechanism of a drilling rig. It is essentially a large winch with drill line and is used to raise or lower the drill string in the well. It is powered normally through two motors (the power mechanism depends on the type of the rig)."},{"value":"Drilling break","id":"213","desc":"A sudden change in the rate of penetration of the bit without many changes to the bit condition or other drilling parameters. An increase in the drilling rate is a warning sign of high pressure reservoirs and the possibility of a kick (formation fluids entering a wellbore)."},{"value":"Drill collar","id":"214","desc":"Drill collars (DCs) are heavy, thick-walled steel tubes with threaded connections cut (not welded) on both ends. The primary role of the drill collars is to provide weight on the bit (compression load) for drilling. They are designed to withstand down hole conditions while under compression as well as under tension. The bore of a drill collar is accurately machined to ensure smooth, balanced rotation. Collars are manufactured in a wide range of sizes (ODs) and are generally used in Range 2 lengths - 9?15 - 9?76 m. Drill collars are used to provide Weight on Bit (WOB) and in combination with other components of the BHA to provide directional control."},{"value":"Drill collar sub","id":"215","desc":"A crossover sub used to connect drill collars with drill pipe."},{"value":"Drill floor","id":"216","desc":"It is also called rig floor or derrick floor. See rig floor"},{"value":"Drilling fluid","id":"217","desc":"Drilling fluid is one of the most critical components required for drilling a well. It has got several functions but the primary functions of a drilling fluid are to lift cuttings of the wellbore to surface so that the hole is cleaned properly, to exert adequate hydrostatic pressure on the formation so that the entry of formation fluids into the wellbore is prevented (it is the primary well control mechanism) and to lubricate the bit. There are several types of drilling fluid ? water based mud, synthetic oil based mud, oil based mud. Even air and foam are used as drilling fluid on certain applications. See also mud."},{"value":"Drill-in fluid","id":"218","desc":"A type of drilling mud specially designed to minimize formation damage and is used when drilling through reservoir sand. This is not used in all the wells but only used if specifically required where the normal drilling mud cannot be used."},{"value":"Drilling line","id":"219","desc":"It is a wire rope that is reeved on the draw works which is used to raise or lower the drill string. See also drawworks."},{"value":"Drilling mud","id":"220","desc":"It is also called drilling fluid or simply mud. See drilling fluid, mud."},{"value":"Drilling rig","id":"221","desc":"See rig."},{"value":"Drill pipe","id":"222","desc":"Drill pipe is a seamless tube, equipped with special threaded couplings at the ends called tool joints. It is used to transmit rotary power from the surface to the bottom of the hole and to supply fluid at sufficient volume and pressure to the bit. Drill pipes are designed for tensile load. Most of the drill string is made of drill pipe and hence more the depth of the well, more is the tension on the pipe that is near the surface. Drill pipes are run between the Kelly or top drive at surface and HWDP\/drill collars at the bottom of the string near the bit. Drill pipe joints are available in three ranges of length - 18 to 22 feet (5.5 to 6.7 meters), 27 to 30 feet (8.2 to 9.1 meters), and 38 to 45 feet (11.6 to 13.7 meters). The most popular length is around 9 to 9.5 meters. It is available with outside diameters (nominal) ranging from 2.3\/8? to 6.5\/8?."},{"value":"Drill pipe protector","id":"223","desc":"A specially made rubber protector that is attached around the drill pipe so that during rotation while drilling wear on casing is minimised ore prevented. The protectors should not be run on open hole."},{"value":"Drill pipe rubber or drill pipe wiper","id":"224","desc":"This is used when the drill pipes are being pulled out of hole. It is a rubber or elastomer disk that is placed around a joint of drill pipe and is held stationary below the rotary table. As pipe is removed from the well, the rubber wipes the mud off the outside of the pipe allowing the pipe to come out to the rig floor dry minimizing wastage or spillage of mud."},{"value":"Drill pipe safety valve","id":"225","desc":"It is a full opening safety protection valve with the same threads that of the drill pipe and that is made up between the Kelly and drill pipe or top drive and drill pipe. It is used to shut the inside of the drill string to prevent any backflow during a kick."},{"value":"Drill ship","id":"226","desc":"A self-propelled floating drilling unit which is basically a ship on which drilling unit is installed. Drill ships are capable of drilling in water depths as low as 40 m to as deep as 10,000 m. Anchored or moored ships are used only up to a water depth of 1,500 m.Beyond that depth, dynamically positioned ships are used."},{"value":"Drill pipe slips","id":"227","desc":"see slips."},{"value":"Drilling rate","id":"228","desc":"It is the speed with which the bit drills the formation, usually called the rate of penetration. It is defined generally in units of length per unit time or time per unit length."},{"value":"Drill stem","id":"229","desc":"It is the term used for referring all the components that form a drill string in sequence from kelly or top drive at the top to drill pipe, subs, drill collars above and below drilling jars, jars, stabilisers, subs, other specialty items and bit at the bottom. This sequence may be different for other strings say for a highly deviated ERD (extended reach) well or horizontal well where some times drill collars are not used above the bit. See also drill string."},{"value":"Drill stem test (DST)","id":"230","desc":"Drill stem test is a method of testing the well that means allowing the reservoir fluid to flow to the surface under controlled conditions. DST confirms many aspects of the reservoir including but not limited to productivity, deliverability, reservoir characteristics, reservoir boundary, sampling etc. A proper drill stem test string consist of a down hole shut in valve, annulus pressure operated valves and a packer. The packer is set above the perforated zone and the well is activated with the necessary under balance. The well flows to surface through the tubing which is controlled at surface by surface testing equipment which includes a production head and a choke."},{"value":"Drilled solids","id":"231","desc":"There are fine particles in the drilling mud finely ground\/drilled by the bit.\n\n"},{"value":"Drill string","id":"232","desc":"This is same as drill stem. See drill stem."},{"value":"Drill string float","id":"233","desc":"It is check valve that allows only one way of circulation and is placed just above the bit. It allows mud and other fluids to be pumped in to the well but it will prevent any flow entering the drill string."},{"value":"Drill-off test","id":"234","desc":"It is a common method to determine the best or optimum weight on bit to achieve the best drilling rate."},{"value":"Drive","id":"235","desc":"The mechanism in which the energy required for the production of reservoir fluids by its own energy is provided. Drives can be of many types ? water drive, solution gas drive etc."},{"value":"Dry hole","id":"236","desc":"A dry hole generally means no oil or gas present in it but only water. Sometimes a hole can called dry even if contains oil but not of commercial quantities."},{"value":"Dual completion","id":"237","desc":"A single well that producer from two different reservoir sections using one tubing for each reservoir. One string is called long string which is run to the bottom reservoir and the other is called short string which is run to the upper reservoir. The production from each zone is segregated by the two strings thereby preventing co-mingling of the zones."},{"value":"Dynamic positioning","id":"238","desc":"A method for keeping a floating rig in station without anchors using thrusters."},{"value":"Edgewater drive","id":"239","desc":"Water drive is a reservoir drive mechanism in which oil is driven through the reservoir by an active aquifer. Water drive is mainly of two categories ? edge water drive and bottom water drive. In edgewater drive the water is available only at the edges or flanks of the reservoir whereas in the bottom water drive, the water is present under the oil accumulation."},{"value":"Effective permeability","id":"240","desc":"When more than one fluid is present in the reservoir rock, then the ability of one of the fluid to flow through the rock is called the effective permeability."},{"value":"Effective porosity","id":"241","desc":"The interconnected pore spaces or connected pore volume that contributes effectively to fluid flow or permeability in a reservoir rock. Effective porosity does not include isolated pores that are unconnected. It is effectively less than the total porosity."},{"value":"Electric well log","id":"242","desc":"The electric log is run a wire line in a well to record formation characteristics like resistivity, density, porosity etc through electric signals. The data is used to identify the type of rock and presence, nature, thickness of hydrocarbons, depth at which they are present, contact between hydrocarbon and water etc. It is also called wireline logging."},{"value":"Electrical submersible pump (ESP)","id":"243","desc":"An artificial lifting system that uses a pumping mechanism downhole, which is driven by electric power. The ESP has several stages of centrifugal pump sections that are configured specifically to suit the completion requirements."},{"value":"Electromagnetic propagation tool (EPT)","id":"244","desc":"An electric log that is used to measure di-electric constant of formation fluids to distinguish between oil and water. The tool uses or emits electromagnetic micro waves in to the formation as a mean to measure the di-electric constants and hence the name."},{"value":"Elevation","id":"245","desc":" It is the vertical height of one point on the earth above a datum point as reference, usually mean sea level."},{"value":"Elevators","id":"246","desc":"elevators clamp around a pipe (casing or drill pipe or tubing) so that the pipe can be raised from or lowered into the hole. The elevators are connected to the links, which in turn is connected to the hook, traveling block and the drill line. So when the draw works is operated, the raising or lowering action takes place. See also draw works."},{"value":"Emulsion Mud","id":"247","desc":"It is water based drilling mud, which contains dispersed oil or synthetic hydrocarbon as an internal phase."},{"value":"Enhanced oil Recovery","id":"248","desc":"This is a third stage recovery mechanism for oil and gas production, which begins at the end of the secondary recovery process or at any time appropriate during the life of the reservoir. This is an advanced method that goes beyond conventional primary and secondary recovery techniques. Chemical\/polymer flooding, miscible hydrocarbon displacement and carbon-di-oxide injection and thermal recovery\/steam injection are the most common enhanced oil recovery process. Popularly called as EOR."},{"value":"Entrained Gas","id":"249","desc":"The gas from the formation that enters the drilling mud is called entrained gas."},{"value":"Eocene","id":"250","desc":"It is an epoch or era in tertiary period between Paleocene and Oligocene epochs."},{"value":"Equivalent circulating density (ECD)","id":"251","desc":"When the mud is circulated in a well, the pressure losses that happen at the annulus from the bit to the surface exerts an additional pressure at the bottom over and above the hydrostatic pressure of the mud. This pressure is converted to density and added to the mud density to give the equivalent circulating density."},{"value":"Ethane","id":"252","desc":"It is light gas under atmospheric conditions and one of the components of natural gas with chemical formula C2H6."},{"value":"Exploration Well","id":"253","desc":"The exploration well is drilled to confirm the presence of hydrocarbon in the well. The well is selected or matured from an inventory of prospects and leads, which were made, based on subsurface work that includes geophysical and geological work with 2D or 3D seismic data and offset wells."},{"value":"Extenders","id":"254","desc":"It is a substance added to mud to increase viscosity without adding clay or other viscosifying material. Substances used in cementing applications to increase the yield of cement are also called extenders."},{"value":"Extended reach well (ERD Well)","id":"255","desc":"Extended reach wells were evolved from directional drilling to horizontal, then lateral, then multi-lateral step outs to achieve horizontal well departures or reaching a subsurface location at long distances with horizontal displacement to true vertical depth ratios beyond the conventional experiences. Generally ERD is defined if the ratio of horizontal displacement to true vertical depth is greater than 2. However local ERD experience may create different scale levels for defining ERD wells."},{"value":"External upset end","id":"256","desc":"This refers to drill pipe or casing or tubing connection in which the inside diameter remains constant where the connection between two pipes are made, but the outside diameter is enlarged to accommodate the threaded connection as well as to sustain or increase the connection strength to that of the pipe body."},{"value":"Fann V-G meter","id":"257","desc":"A device used to measure or estimate the rheology, plastic viscosity, yield point and gel strengths of the drilling mud by recording the values at different rpm (rotations per minute). Fann V-G meter is a commercial name of a device"},{"value":"Fault","id":"258","desc":"A break or fracture in a rock along which there is a displacement such that one side of the rock has moved either vertically up or down or laterally or diagonally relative to the other side. "},{"value":"Female connection","id":"259","desc":"The threads at the box end of a pipe. The connection is called female as threads are made inside of the box so that a male connection can be joined to it."},{"value":"Filter cake","id":"260","desc":"While drilling a well across permeable formations like sand, the drilling mud forms a layer of concentrate solids at the walls of the permeable formations while filtration loss happens at the permeable formations. This layer is called filter cake or sometimes as wall cake or mud cake"},{"value":"Filter cake thickness","id":"261","desc":"It is a measurement of the thickness of the filter cake formed at the walls of the permeable formations in a well (see filter cake). Standard API test indicate the thickness in 30 seconds of an inch during a 30 minute test."},{"value":"Filtration or fluid loss","id":"262","desc":"The loss of liquid phase of the drilling mud in to the formation against a permeable zone when a filter cake was formed. Filtration losses can happen both in static and dynamic conditions. As the filtration loss property of the drilling mud has direct bearing on the drilling rate, hole problems and formation damage in sensitive reservoirs and differential sticking across permeable zones, extensive emphasis is placed on filtration loss and to control it."},{"value":"Fish","id":"263","desc":"It refers to any object that is left or dropped in a well during drilling or work over or any other operations. Unless the object is removed the operations cannot continue or proceed. The fish can be anything from a scrap to a pipe, which is part of the drill string or completion string. Fishing operations are expensive and they add to a 100% non-productive time sometimes leading to abandoning of the well if the fish cannot be retrieved or sidetracking of the well with additional expense."},{"value":"Fishing string","id":"264","desc":"It is a string made up at the bottom with the fishing tool (overshot, reverse circulation junk basket, magnet etc) and assembly (fishing jar, bumper sub, safety joint etc) and run on drill pipe to catch and retrieve the fish out of hole."},{"value":"Float collar","id":"265","desc":": It is a special short device with threads of the casings it is run with and is installed generally after one or two or three joints of casing from the float shoe (which is at the bottom). The float collar has a check valve, which allows circulation on only one direction. This helps to prevent mud entering the casing while running in hole, thereby making the casing float and thus reducing the weight and also prevents any back flow of cement during cementing operations. This is the place where the cementing bottom and top plugs would land."},{"value":"Float shoe","id":"266","desc":"It is a special short device with threads of the casings on one side and rounded at the bottom with an opening as per the design. It is also a check valve similar to float collar and its functions. As the bottom is rounded it is used to guide the casing while running in hole. There is another type of shoe that has a differential fill up mechanism and it fills up the casings while running in hole automatically."},{"value":"Flocculation","id":"267","desc":"The suspended particles in a drilling mud coagulate together due to attractive forces between them. Flocculation sometimes used to remove fine, low density solids from drilling mud. To achieve flocculation (i) salt is added to increase the electrolyte concentration or (ii) a polymeric flocculent is added. Most of the times flocculation is not preferred and by various methods the mud is deflocculated. See deflocculation."},{"value":"Flocculating agent","id":"268","desc":"A chemical or material that is used to enhance the flocculation or coagulating of suspended solids in a drilling mud."},{"value":"Flow rate","id":"269","desc":"It generally refers to the volume per unit time through a tube, pipe or vessel, say gallons per minute, m3 per hour, barrels per day."},{"value":"Fluid-loss additive","id":"270","desc":"A chemical or additive used to reduce the filtration loss in a drilling mud."},{"value":"Foam drilling","id":"271","desc":"During air drilling, when the water production exceeds a limit, the capacity of compressors and air circulating system is not adequate to remove the water from the well. Also cuttings stick together clogging the annulus and often drill pipe sticking is the result of this effect. In this situation, foam or mist drilling is initiated. A foaming agent, a chemical similar to soap and when added to water it forms a mist or foam (it causes the water in the well to foam and froth). As the foam is lighter than water, the system requires less air pressure to move the water up in the hole"},{"value":"Formation","id":"272","desc":" It is a basic unit of naming rocks in stratigraphic nomenclature. A set or bed or deposit of rocks with a distinctive feature of homogeneous lithology which are or once were horizontally continuous or composed throughout substantially of the same kind of rock and large enough so that it can be mapped. Each formation is given a name based on studies and understanding."},{"value":"Formation breakdown","id":"273","desc":"The breaking down or fracturing of the formation due to excessive pressure applied on it."},{"value":"Formation breakdown pressure","id":"274","desc":"The pressure at which a formation will breakdown o fracture"},{"value":"Formation damage","id":"275","desc":"The damage normally refers to a reduction in permeability of a reservoir rock or productivity of the formation caused by the invasion of drilling fluid and treating fluids to the section adjacent to the wellbore. It is often called skin damage."},{"value":"Formation dip","id":"276","desc":"The angle of the formation bed at which it inclines away from the horizontal"},{"value":"Formation fluid","id":"277","desc":"Fluid (gas, oil or water) that exists in the pore spaces of a rock formation"},{"value":"Formation pressure","id":"278","desc":"This is the pressure of the fluids present in the formation. This is also called reservoir pressure."},{"value":"Formation strength or competency or integrity","id":"279","desc":"The ability of the formation to withstand applied pressure. After a casing it set, generally before drilling the next hole section, formation integrity is tested and recorded (see also Leak off test ? LOT)."},{"value":"Formation water","id":"280","desc":"Water that is present in the pore spaces of the formation."},{"value":"Fourble","id":"281","desc":"Four singles of drill pipe or tubing joined together forms a fourble. See also double and thribble."},{"value":"Fourble board","id":"282","desc":": It is a working platform of the derrick man located on the mast of a rig to handle fourbles (four singles of drill pipe or tubing). It is also called monkey board."},{"value":"Fracture","id":"283","desc":"A crack or crevice in a formation, either natural or induced. For fracturing, see hydraulic fracturing."},{"value":"Fracture gradient","id":"284","desc":"It basically indicates the pressure at which the formation will get fractured. The value is converted in to a gradient ? psi\/ft as it is convenient to use."},{"value":"Free point indicator","id":"285","desc":"When a pipe is stuck in the hole, free point indicator helps to determine the deepest point above which the pipe is free. The tool measures the amount of strain on the pipe due to stretch\/overpull, which is then used to determine the depth at which the pipe is stuck."},{"value":"Funnel viscosity","id":"286","desc":"For convenience and for quick evaluation of the viscosity of the mud, on the rigs a Marsh funnel is used. It is a funnel of 1 litre capacity and the time taken for 1 litre of drilling mud to flow through the funnel is measured and is reported as Funnel viscosity."},{"value":"Gamma ray log","id":"287","desc":"It is type of nuclear log that records natural radioactivity for the given formation nuclear radiation around the wellbore and is used to identify different rock formations like sandstone or shale. Shales normally produce high gamma ray values whereas sands produce low values."},{"value":"Gas cap","id":"288","desc":"Gas that exists in gas phase above oil or water in a reservoir. If it is above oil, it is normally a saturated oil pool. A gas-oil contact is represented to show the separation of the gas from the oil reservoir. The gas cap can be primary or secondary in nature."},{"value":"Gas cap drive","id":"289","desc":"A drive mechanism in which the pressure of the gas or expansion of the gas above the oil provides the energy and pushes the oil through the reservoir in to the wellbore for production"},{"value":"Gas chromatograph","id":"290","desc":"An analytical instrument that is used to identify different fractions in a gas."},{"value":"Gas condensate reservoir","id":"291","desc":"A reservoir that contains hydrocarbon in gas phase under initial pressure and temperature conditions. As the gas is produced, it starts yielding condensate liquid at surface. Retrograde gas condensate reservoirs also exist in gas phase initially and during gas production, when the reservoir pressure falls below the dew point (at the same temperature), liquid hydrocarbons (condensate) separate from the gas by condensation. Production of the retrograde gas condensate reservoir is complex especially after the reservoir pressure reaches the dew point as the productivity of the reservoir is affected due to the formation of liquid hydrocarbons at the reservoir and reduction of permeability near the wellbore."},{"value":"Gas hydrates","id":"292","desc":"Gas hydrates are gas molecules trapped in ice. A gas hydrate is a solid crystalline compound. It occurs naturally in permafrost areas or at sea bed in deep water zones. It may also be formed at surface when suddenly cooled while passing through chokes and blocks the pipes or pipelines at the downstream side of the chokes. Gas hydrates are melted or removed by heating the pipes or pipelines or by injecting ethylene glycol."},{"value":"Gas injection","id":"293","desc":"Injection of gas into formation to maintain the reservoir pressure or to free oil trapped in pore spaces by becoming miscible with it and enhance the recovery of oil. "},{"value":"Gas lift","id":"294","desc":": It is an artificial lift used to enhance the production of oil. Compressed gas is pumped in to the well, through a gas lift mandrel\/valve into the production tubing, to lift the produced hydrocarbon liquid to the surface."},{"value":"Gas oil contact","id":"295","desc":"The boundary that separates the gas phase from the oil in a saturated oil reservoir. It is not a simple line but it extends several feet where the high saturation of oil changes gradually to high saturation of gas. However, the contact generally flat or horizontal. This signature is called direct hydrocarbon indicator and is one of the indicators that geoscientists look for to find hydrocarbons during seismic interpretation (geologists love the word ?flat spots?)."},{"value":"Gas oil ratio or GOR","id":"296","desc":"This is generally related to associated gas (AG) or saturated gas in oil reservoir. It is the amount of gas that is liberated from oil during the trip of oil from the reservoir to surface through production tubing and is represented as standard cubic feet\/stock tank barrel (scf\/stb) or m3\/m3."},{"value":"Gas reservoir","id":"297","desc":"Refers to a reservoir that contains only gas as a single phase."},{"value":"Gel strength","id":"298","desc":"It is a measure of attractive forces within the drilling fluid under static conditions. The gel strength is time dependent and is disrupted once the circulation or flow is initiated. Gel strength indicates the ability of the mud to hold solids in suspension when the circulation is stopped and mud becomes static"},{"value":"GPM","id":"299","desc":"It is a unit for flow rate and is defined as volume per unit volume. GPM is gallons per minute"},{"value":"Galena (PbS)","id":"300","desc":"Its chemical name is lead sulfide. It is used as a weighting material to increase the density of mud especially for heavy muds. Normally barite is used as a weighting material as it is cheaper and readily available but barite has limitations beyond a certain mud density and so Galena is used beyond that range. "},{"value":"Gas-cut mud","id":"301","desc":"While drilling sometimes gas from the formation gets dissolved or entrained in the mud. Gas cut mud can reduce the bottomhole pressure slightly and hence must be removed to prevent a kick. It also affects the mud pump efficiency. Poor boy degasser is used to remove the gas from gas cut mud. Sometimes as a secondary unit, a vacuum degasser may also be used."},{"value":"Gauge hole","id":"302","desc":"A gauge hole terms represents that he diameter of the hole is same as the diameter of the bit."},{"value":"Geopressure","id":"303","desc":"Geopressure is a reservoir pressure that is higher than normal pressure. It is abnormal high pressure formation, which occurs in isolated reservoirs and may not be connected to other reservoirs"},{"value":"Geopressured shales","id":"304","desc":"Impermeable shale formations at abnormal pressures than normal that causes the shale to slough or cave if the mud weight is lower than the pressure of the shales."},{"value":"Geostatic pressure","id":"305","desc":"It is pressure exerted on a rock by the weight of the overlying rocks. It is also called overburden pressure."},{"value":"Geothermal gradient","id":"306","desc":" It indicates the increase in temperature per unit depth in the earth. It is generally measured in 0C\/m or 0F\/100 ft and varies between 1.50-2.30F\/100 ft but specifically it may be lower and higher than the range given"},{"value":"Geologic time scale","id":"307","desc":"Geologic time scale run through billions of years and in order to define the times of the past physically, the time scale was categories in to eras (like Cenozoic, Mesozoic, Paleozoic, and Precambrian), which are subdivided into periods and epochs (like tertiary, cretaceous, Jurassic etc). The rock once its age is determined is referred to based on the era or period like rock of Jurassic period."},{"value":"Geophysical exploration","id":"308","desc":": It is a study or survey to determine or evaluate certain properties of the earth to locate subsurface information such as structure of different type of rocks, possibility of hydrocarbon accumulation or other minerals or to make other practical applications. In the oil and gas industry, the most common studies are seismic, magnetic and gravity surveys."},{"value":"Granite","id":"309","desc":"It is an intrusive igneous rock mostly formed by melting of rock deep in the crust or mantle such that the molten material being light moves up towards surface but gets cooled and solidified before reaching the surface. Granite mainly consists of quartz, feldspar and other minerals in small fractions like magnetite, topaz, garnet etc. Hydrocarbon presence in commercial quantities are found in fractured granites."},{"value":"Gravel packing","id":"310","desc":"It is a method of sand control. During production, some reservoirs are not competent enough to hold the sands thereby resulting in sand production along with the oil or gas. Sand production is detrimental to hydrocarbon production, downhole and surface equipment. Gravels are packed across the reservoir sands near the well bore such that the sands are prevented to enter the wellbore allowing only hydrocarbons to be produced."},{"value":"Gravity drainage","id":"311","desc":": It is one of the drive mechanisms to produce oil or gas. In this drive, gravity is used for drainage of the reservoir fluids. In the absence of a water drive or a gas drive, gravity drainage is an important source to provide the energy to produce oil or gas. This is a slow process and is most effective in thick reservoirs with high vertical fluid communication and thin reservoirs with appreciable angle of dip and favorable permeability to flow in the vertical direction."},{"value":"Guar gum","id":"312","desc":"Guar gum is a polymer used to viscosify the drilling mud or to prepare clay free drilling muds. However, as it starts degrading at 1500 F temperatures, its use it limited to shallow depths only."},{"value":"Gunk plugs","id":"313","desc":"Diesel oil bentonite plugs are called gunk plugs. Gunk plugs are generally used to plug extreme losses or even an underground blowout. Bentonite is held in suspension in diesel until the plug is placed across the loss zone and then arranging water to come in contact with bentonite which hydrates rapidly to become extremely viscous. In the underground blow out zone, this is not a permanent solution but provides the necessary time to set up a permanent plug like cement"},{"value":"Gypsum lignosulfonate mud","id":"314","desc":"These are used along with bentonite based mud system to drill through gypsum and anhydrite zones. As the bentonite based system were getting highly contaminated drilling through gypsum and anhydrite formations, the muds were stabilized at surface by adding the gypsum and lignosulfonate. Later their use extended to stabilize moderately reactive shales."},{"value":"Gypsum polymer mud","id":"315","desc":"This mud provides high concentration of calcium ion to create inhibition and to stabilize reactive shales."},{"value":"Hanging wall","id":"316","desc":"Generally in a normal fault, the downthrown side of the fault is called hanging wall."},{"value":"Hard banding","id":"317","desc":"The tool joints of a drill pipe undergo wear when the pipe is rotated down hole while drilling. Hard banding is a special wear resistant material that is applied to the tool joints to prevent the wear due to abrasion."},{"value":"Heavyweight drill pipe","id":"318","desc":"Referred as HWDP, they are a type of drill pipe but with thicker walls and longer tool joints and an integral wear pad in the middle. It is generally used as a transition between drill collars and drill pipes, to make the crossover from compression load to tensile load gradually as HWDP is more resilient to fatigue than standard drill pipe, especially in compression. "},{"value":"Hoist","id":"319","desc":"It is generally an arrangement of pulleys and wire rope or chain used for lifting heavy objects. Hoists are normally a winch or similar device. On the rig apart from winches, draw works is a big hoist with a high capacity to hoist to lower heavy loads of drill string"},{"value":"Hoisting system","id":"320","desc":"Hoisting system comprises of draw works, crown block, traveling block, hook and drill line. The main purpose of the hoisting system is to lift and lower the drill string or casings or tubings out of and into the well respectively"},{"value":"Hole","id":"321","desc":"In drilling, it refers to the wellbore or borehole"},{"value":"Hole angle","id":"322","desc":"The angle at which a hole deviates from vertical."},{"value":"Hole cleaning","id":"323","desc":"Hole cleaning is an important and critical step in drilling wells safely and effectively. It means to keep the hole clean at all times by effectively and timely removing the cuttings generated while drilling from the bottom of the bit as well as from the well. In vertical wells, the hole cleaning efforts are focused on reducing the settlement of cuttings and to prevent annulus loading with cuttings. In deviated wells, the efforts are focused on efficient removal of cuttings bed and drag them in to suspension in mud so that they can be effectively removed to the surface. Improper hole cleaning leads to most of the stuck pipe incidents in drilling."},{"value":"Hole sizes","id":"324","desc":"Refers to the size of the well. A well starts from a higher size of hole at the surface and reaches a lower size of the bit at the bottom of the well tapering to the next lower size after every casing is run and cemented. For example, a 3 casing policy of a well design indicates that the well will start with 17.1\/2? hole which will be cased and cemented with 13.3\/8? casing followed by a 12.1\/4? hole in which 9.5\/8? casing is run and cemented. The next phase will be an 8.1\/2? hole in which a 7? casing will be run and cemented."},{"value":"Hopper","id":"325","desc":"Hoppers are used to mix mud in a rig. It is a cone shaped device, which has a large opening on the top with a narrowed bottom. The dry chemicals are poured from the top. The drilling mud is injected through a nozzle\/venturi system at the bottom creating a suction effect by which the dry chemicals are sucked in. The mud and dry chemicals get mixed and taken to tank through a discharge line."},{"value":"Horizon","id":"326","desc":"It refers to a distinct layer or a group of layers of rock."},{"value":"Horizontal drilling","id":"327","desc":"If a well is drilled with zero deviation from vertical, it is called vertical well. If the well is drilled with certain deviation from the vertical then it is called deviated well (see deviation and directional drilling). In horizontal drilling, the well is drilled such that the deviation of borehole is 900 from the vertical and it looks horizontal\/parallel to the formation from an elevation view (sometimes deviation greater than 800 is considered as horizontal in drilling terminology). Horizontal wells are drilled for many advantages and reasons. Some of them are:\n? Longer horizontal drain hole increases the exposure of the pay zone\n? Allows high production rates at lower draw down (less coning)\n? Naturally fractured reservoirs (vertical or deviated wells are notoptimal to intersect allthe fractures efficiently)\n? Reduced number of development wells\n? Thin reservoir sections (< 30 feet) especially with bottom water drive\n? Thick oil or tight reservoirs to improve productivity\n\n"},{"value":"Hydrates","id":"328","desc":"see gas hydrates."},{"value":"Hydraulics","id":"329","desc":"In drilling the hydraulic system is the drilling mud and hydraulic design refers to effective utilization of drilling mud to serve many purposes as an improperly designed hydraulics system can slow down the drilling rate, fail to clean or remove cuttings effectively from the hole etc. The primary purposes of a good hydraulics system are : (i) control subsurface pressures by adequate mud density, (ii) remove cuttings from the well effectively and keep the well clean, (iii) increase drilling rate (iv) minimize surge and swabbing pressures etc."},{"value":"Hydraulics fracturing","id":"330","desc":"Generally used to crack or fracture a tight (low permeable) formation to enhance the oil or gas production. Specially blended liquid with sand grains, aluminum pellets, glass beads etc are carried in suspension and pumped down in to the formation and under high pressure the formations crack open. When the pressure is released at surface, the fractures partially close on the materials allowing channels for oil to flow through them to the well."},{"value":"Hydraulic horsepower","id":"331","desc":" It is a measure of the work required to push mud through the bit nozzles, which is related to the removal of cuttings from below the bit."},{"value":"Hydraulic impact force","id":"332","desc":"It is a measure of the force exerted by the drilling mud at the exit of the bit nozzles."},{"value":"Hydrocarbons","id":"333","desc":"Hydrocarbons are organic compounds made of carbon and hydrogen atoms. They come with many combinations from gas as the lighter form to solid as the heavier form. Petroleum is a mixture of different hydrocarbons. For example, Methane is a gas hydrocarbon with formula CH4. Propane when liquefied becomes LPG (in combination with Butane) is C4H10."},{"value":"Hydrogen embrittlement","id":"334","desc":"due to absorption of hydrogen gas, the ductility of a metal is reduced or lowered. In drilling, it happens if the hydrocarbon bearing formation has hydrogen sulfide present. This term is called acid brittleness."},{"value":"Hydrogen sulfide","id":"335","desc":"it is a compound of hydrogen and sulfide (H2S). It is a flammable, colorless gaseous compound, which in small amounts has the odor of rotten eggs. At some areas, it is found in petroleum causing foul smell and reducing the value of oil. In high concentrations, it is extremely corrosive and most critically is poisonous causing damage to skin, eyes and breathing to seriously the nervous system, lungs and heart and ultimately death. At large concentrations, it deadens the sense of smell and hence if a person is in the midst of high concentrations of H2S he may not be aware as the smell senses are dead. A special and certified training is given to all the personnel working in suspected H2S areas"},{"value":"Hydrogen sulfide cracking","id":"336","desc":"when metals are exposed to hydrogen sulfide gas, some type of corrosion occurs leaving minute cracks just under the surface of the metal."},{"value":"Hydrostatic pressure","id":"337","desc":"It is the force exerted at a particular depth by a fluid, which is at rest. It depends only on the density of the fluid and the true vertical depth. Its unit is mass per unit area. General units are pounds per square inch (psi), kilo Pascal (kPA) etc. In drilling, is refers to the hydrostatic pressure of the drilling mud or brine or any other drilling or completion fluid"},{"value":"Hydrostatic head","id":"338","desc":"see hydrostatic pressure."},{"value":"IADC","id":"339","desc":"International Association of Drilling Contractors. www.iadc.org."},{"value":"Insert bit or tungsten carbide insert bits","id":"340","desc":"A roller cone bit of bit where tungsten carbide inserts or buttons are pressed in to the cones. The tungsten carbide inserts provide longer tooth life as compared to steel tooth bits."},{"value":"Internal upset end","id":"341","desc":"This refers to drill pipe or casing or tubing connection in which the outside diameter remains constant where the connection between two pipes are made. The pipe has an extra-thick inside wall to accommodate threading without affecting the outside diameter."},{"value":"Invert emulsion mud or invert oil mud","id":"342","desc":"An oil base drilling mud in which oil or water in oil emulsion is the continuous phase. Although oil based muds and invert emulsion muds are essentially same with difference only in the percentage of water by volume (oil based mud less than 5% water), essentially both are same."},{"value":"Igneous rock","id":"343","desc":"Igneous rocks are rocks formed by solidification of cooled molten rock (or magma) either below the surface as intrusive plutonic rocks or on the surface as extrusive volcanic rocks."},{"value":"Impermeable","id":"344","desc":"A formation may be porous but devoid of any interconnected pores thereby becoming impermeable which does not allow passage of any fluid to flow through it. Shale is an impermeable rock and they make a good cap rock to hold accumulation of oil or gas"},{"value":"Impression block","id":"345","desc":"A block made of lead or a soft material at the bottom. It is run on drill pipe to identify the configuration of top of a fish in a well. It is run and allowed to rest on top of the fish with some weight so that an impression can be made. When it is pulled out, the shape, size and position of the fish is determined so that an appropriate fishing tool can be run to retrieve the fish."},{"value":"Inclination","id":"346","desc":"Angle of the well from the vertical. See drift angle"},{"value":"Independent wire rope core (IWRC)","id":"347","desc":"A core of wire rope consisting of a strand of steel wires spiraled with each other to provide a single wire rope."},{"value":"Induction log","id":"348","desc":"An electric well log, which uses electromagnetic wave to measure conductivity of the formation. As hydrocarbon bearing formations are less conductive or more resistant than water, an induction survey helps to identify the formation fluids. As inverse of conductivity is resistivity, the formations can be identified easily"},{"value":"Internal yield pressure","id":"349","desc":"See burst pressure"},{"value":"Injection well","id":"350","desc":"A well which is used to inject water to a subsurface strata either for disposal of produced water after treatment or for pressure maintenance of a producing reservoir."},{"value":"Inside blow out preventer or inside BOP","id":"351","desc":"It is a short collar having the threads of drill pipe with a spring loaded check valve inside. It allows flow in only one direction i.e. down the drill string and does not allow any flow from the well into the pipe. It is used as an emergency system if a kick occurs while tripping the pipe to shut off the drill pipe preventing any formation fluids entering the drill string"},{"value":"Interface","id":"352","desc":"The contact surface between boundaries of two liquids, for example interface between oil and water in a reservoir."},{"value":"Intermediate casing","id":"353","desc":"The casing that is set between the surface casing and production casing. This casing is set at a depth to seal of troublesome formations and to have adequate strength and provide protection to drill the well safely through the reservoir section and set the production casing."},{"value":"Internal upset end","id":"354","desc":"This refers to drill pipe or casing or tubing connection in which the outside diameter remains constant where the connection between two pipes are made. The pipe has an extra-thick inside wall to accommodate threading without affecting the outside diameter."},{"value":"Isopach map","id":"355","desc":"A contour connects points of equal depths or thickness. An isopach map is made of contours to display the stratigraphic thickness of a rock layer or formation as opposed to the true vertical thickness. It is widely used to estimate in-place volumes, understand the gradient of the strata from the crestal level to contact level (example oil-water contact), for well positioning and well engineering etc."},{"value":"Jackup drilling rig","id":"356","desc":"A mobile bottom supported offshore drilling rig. The rigs are designed in water depths up to 120 m (or even more). Although the minimum water depth is an average of 6 to 7 m, few shallow jack up rigs operates in lesser water depths. The jack up rigs has 3 or 4 legs depending upon the design. They are two types of jack up rigs ? mat supported and independent legs. In mat supported jack up rig, the three legs join to a large mat at the bottom, which covers the sea floor area larger than that of the rig?s hull. It is used for very soft unconsolidated seabed conditions. In independent leg jack up rigs, each leg is fitted with a spud can at the bottom. They load of the rig is distributed evenly to each of the spud can. Most of the jack up rigs are not self propelled and hence must be towed by a boats. During the towing, jack up rigs float at the hull with the legs fully extended above the hull. At the drilling location, the legs are lowered to the seabed, which continues to elevate the hull to the desired air gap (clearance above the water). The spud cans of each leg penetrate the seabed until the acceptable or designed point of refusal. Mat supported rigs settle at the bottom of the seabed"},{"value":"Jar","id":"357","desc":"A percussion tool operated mechanically or hydraulically to deliver a heavy downward (or upward) blow to a fish stuck in the borehole. Jar is a very important and critical tool in drilling. Most of the drill strings are run with a drilling jar. Fishing jars are run only when a fish had to be retrieved from the well."},{"value":"Jar accelerator","id":"358","desc":"A tool used in conjunction with jars to increase the power of the hammer blow."},{"value":"Jet velocity","id":"359","desc":"The velocity of the drilling mud when it moves through the nozzles (jets) of a bit. Jet velocity is an important design factor for achieving optimum hydraulics."},{"value":"Joint","id":"360","desc":"A joint in drilling industry refers to a single of drill pipe or casing or tubing."},{"value":"Joint identifier","id":"361","desc":"A hand held gauge used to determine the type of connections of drill pipe or drill collars or cross over subs."},{"value":"Junk","id":"362","desc":": It refers to any debris lost in a well. It may be a cone of a bit, a parted pipe, and any object that fell into the hole and impedes drilling. They must be fished out of the hole before drilling can continue."},{"value":"Junk basket","id":"363","desc":"Also called boot sub, boot basket and junk sub. See boot sub."},{"value":"Junk mill","id":"364","desc":"A mill used to mill or drill junk or debris in a well"},{"value":"Jurassic","id":"365","desc":"It is a geological time scale period lies within Mesozoic era with an age between 190 to 135 million years. It is categorized as upper, middle and lower with lower as the oldest age. Dinosaurs lived during the Jurassic period but become extinct by the end of the Mesozoic era"},{"value":"Kelly","id":"366","desc":"Kelly is one of the main components of a drill string but used only in combination with a swivel and rotary. It is not required in a top drive rig. Kelly is connected to the swivel at the top and to the drill pipe at the bottom. The Kelly is slipped throu"},{"value":"Kelly bushing","id":"367","desc":"The Kelly is slipped through the Kelly bushing and then rollers that mate with the flat sides of the Kelly. The bushing then is inserted in to the rotary table. The Kelly bushing turns when the rotary table is turned. Due to this the Kelly turns which the"},{"value":"Kelly cock","id":"368","desc":"A full opening safety valve (mostly a ball valve) that is connected to both ends of the Kelly. The bottom one that is connected between the kelly and the drill pipe is called lower kelly cock and the top one that is connected between the kelly and the swi"},{"value":"Kelly hose","id":"369","desc":"See rotary hose."},{"value":"Kelly saver sub","id":"370","desc":" It is generally referred to a sub that is used between the Kelly and the drill pipes. As kelly is used several times to make connections and as it is a very expensive item, the threads of the kelly cannot be allowed to get damage due to frequent connecti"},{"value":"Keyseat","id":"371","desc":"It is one of the well bore geometry related sticking problems in a well. The name comes from the key hole shape the rotating drill pipe cuts in the hole against a dogleg. While pulling out of hole, the drill pipe might pass through but the larger diameter"},{"value":"Keyseat reamer or keyseat wiper","id":"372","desc":"A tool used to clear the keyseat by reaming through it."},{"value":"Kick","id":"373","desc":"It generally refers to the entry of formation fluids into a well bore due to the mud hydrostatic pressure becomes lower than the formation pressure. A kick can be gas or oil or water. The kick has to be controlled immediately by using the secondary contro"},{"value":"Kick fluids","id":"374","desc":"The formation fluids that enter into the well bore due to a kick. It can be gas, oil or water or any other combination"},{"value":"Kick off","id":"375","desc":"It refers to the initiation of deflection from vertical in a deviated or directional well."},{"value":"Kick off plugs","id":"376","desc":"If an open hole has to be side tracked to drill a deviated well, then a kick off cement plug is placed at the planned kick off point. The compressive strength of the cement plug must be higher than that of the formation strength to effectively deflect the"},{"value":"Kick off point (KOP)","id":"377","desc":" In a directional or deviated well, the depth at which the deflection of the hole is initiated."},{"value":"Kick tolerance","id":"378","desc":"It is an important well engineering criterion for casing seat selection. It refers to the maximum amount of kick in volume that can be taken so that the kick can be circulated safely out of the well. Its unit is barrels or m3."},{"value":"Kill","id":"379","desc":"In drilling, kill refers to killing of a well that has encountered a kick or killing a well after the completion of testing or to kill a producing well to commence a well intervention work or work over operation. See also kick."},{"value":"Kill fluid or Kill mud","id":"380","desc":"The drilling mud of the weight (density) required to kill the well. A kick occurs when the drilling mud density is inadequate to exert sufficient pressure above the formation pressure. In order to kill the well, the mud density has to be increased to matc"},{"value":"Koomey unit","id":"381","desc":"Commercial name for an accumulator or BOP control unit. See accumulator"},{"value":"Lead tongs","id":"382","desc":"See also make up or breakout tongs. The pipe tongs suspended from the derrick or mast and hang freely at the rig floor. They are primarily used for making up or breaking up a pipe connection. To make or break the torque on the pipe connection, always two "},{"value":"Leak off test","id":"383","desc":"A test made to determine the formation strength at the casing shoe. Also called as pressure integrity test. This is an important criteria for well engineering, casing design, casing seat selection, kick tolerance calculations and maximum mud weight that c"},{"value":"Ledges","id":"384","desc":"Ledges are formed in inter-bedded formations where the hard formation remains in gauge while the upper softer\/weaker formation enlarges. This happens typically when reactive shale is on top and permeable sand below. If the mud is not designed to combat th"},{"value":"Lifting sub","id":"385","desc":"It is a solid piece of pipe with threads at the bottom to match that of a drill collar or any other pipe with a pronounced upset or shoulder such that an elevator can be latched. It is used to pick up a drill collar or any other pipe using an elevator saf"},{"value":"Lignosulfonate","id":"386","desc":"It is a chemical additive to drilling mud and is manufactured as a by-product in papermaking. It helps to reduce the viscosity, gel strength and fluid loss. It is useful even at high temperatures up to 200 deg C. It affects the mud properties by defloccul"},{"value":"Links","id":"387","desc":"There are two steel rods with ears on both ends used to attach the elevators to the hook of the traveling block. The ears on the top end hang on the hook of the traveling block and those at the bottom are hooked to the elevators. They are also called bail"},{"value":"Lime","id":"388","desc":"A chemical that is primarily composed of calcium oxide (CaO). Lime has various names and types depending upon the composition, chemical and physical forms like quicklime, hydrated lime and calcium carbonate. "},{"value":"Lime mud","id":"389","desc":"Drilling muds that are treated with lime to provide a source rich in calcium. They have good inhibition properties to control swelling or sloughing shales, hole enlargement and excessive viscosity build up due to dispersion of solids in the mud."},{"value":"Limestone","id":"390","desc":"A sedimentary rock, which is rich in carbonates. The two important constituents are calcite and dolomite. Limestone can be organic or clastic and may be fresh water or marine. Limestones are reservoir rocks that can contain oil and gas."},{"value":"Liner","id":"391","desc":"Liner is a casing string but instead of running up to the surface, liners are run from the bottom to the previous casing string. Liner are suspended on the casing string using a liner hanger with an over lap of about 50 to 150 m (this over lap is called l"},{"value":"Liner hanger","id":"392","desc":"A device which is used to hang or suspend a casing string on another casing string. See liner."},{"value":"Liner lap","id":"393","desc":"See liner."},{"value":"Litho-Density log (LDL)","id":"394","desc":"This is an electric log that used gamma ray radioactive source to measure the density of the formation. See density log."},{"value":"Lithology","id":"395","desc":"Refers to general characteristics of sediments, rock types present in a stratigraphic division."},{"value":"Log","id":"396","desc":"Generally refers to a systematic recording of data. There are several logs used in drilling. Mud log, wireline log, driller?s log, etc."},{"value":"Logging","id":"397","desc":"See wireline logging."},{"value":"Logging While Drilling (LWD)","id":"398","desc":"Unlike conventional wireline logging which is run on wireline after the well is drilled to the required depth and the bit is pulled out of hole, logging while drilling measures the reservoir characteristics while drilling the well. The LWD tools are run a"},{"value":"Lost Circulation","id":"399","desc":"This term refers to loss of mud in to the hole when mud is static and partial or total loss of mud returns in a well when the mud us dynamic (under circulation). The loss can happen across coarse permeable formation (sands or gravels) at shallow depths, i"},{"value":"Lost Circulation Material (LCM) or Lost Circulation Additives","id":"400","desc":"It is broadly defined as any material that can stop or reduce the loss of drilling mud in a well by sealing or bridging the loss zones. Generally the loss circulation materials are divided in to ? fibrous materials, flake materials, granular materials and"},{"value":"Lubricator","id":"401","desc":"A casing or tubing pipe fabricated specially to be place above a valve on x-mas tree or tubing head or shooting nipple such that swabbing tools or perforating tools or measurement devices or any other tools can be run in the hole. It provides a means of s"},{"value":"Magnetic north","id":"402","desc":"The north direction in earth?s magnetic field that is indicated by the needle of a magnetic compass."},{"value":"Magnetic single shot survey (MSS)","id":"403","desc":"This is a survey used to determine the angle (deviation) and direction (azimuth) of a well at the measured depth. For running MSS to get angle and direction, a non-magnetic or monel drill collar must be used across the survey depth."},{"value":"Magnetic survey","id":"404","desc":"It is a form of geo-physical survey commonly used. They provide only a general idea of the subsurface geology but as it is cheap, it helps to narrow down the search for most likely areas especially in large fields. A magnetometer usually carried on a truc"},{"value":"Make a trip","id":"405","desc":"A trip refers to either pulling the drill string out of the hole or running the drill string in to the hole in order to perform various operations ? for example to change a bit, to pull out the bit and run casing or to pull out the bit and run a core barr"},{"value":"Make up","id":"406","desc":"Make up in drilling generally refers to making up a string of drill pipe or to screw together two joints of drill pipe."},{"value":"Make up a joint","id":"407","desc":"To screw two joints of drill pipes together."},{"value":"Makeup cathead","id":"408","desc":"A device attached to the cats haft of the drawworks in a rig that is used as a power source to pull the makeup tongs so that torque is applied for screwing and providing final torque to the drill pipe connection. Usually located at the driller?s side of t"},{"value":"Makeup shoulder","id":"409","desc":"The shoulder that is at the end of a pipe or collar. When two joints of pipe or collar are made up, the shoulders have the threads to get screwed together."},{"value":"Make up tongs","id":"410","desc":"Tongs that are used to screw and provide final torque to one section of pipe from another section, especially drill pipe running in to the hole."},{"value":"Male connection","id":"411","desc":"The threads at the pin end of a pipe. The connection is called male as threads are made outside of the pin so that this can be made up to a female connection."},{"value":"Mast","id":"412","desc":"See derrick."},{"value":"Master bushing","id":"413","desc":"It is a part of the rotary table arrangement. The bushing fits in to the rotary table to accommodate the slips (using the appropriate casing bowls inside the master bushing) and also to drive the Kelly bushing to transmit the rotating motion to the Kelly "},{"value":"Measured depth","id":"414","desc":"It is the length measured along the hole. It is denoted by MD. MD may not be the same as vertical depth. In vertical wells, MD and true vertical depth (TVD) will be same but in deviated wells MD will be higher than the true vertical depth (TVD)."},{"value":"Measurement while drilling (MWD)","id":"415","desc":"It is a part of the directional drilling assembly used to measure the deviation and the direction (azimuth) of the hole."},{"value":"Metamorphic rock","id":"416","desc":"It is rock transformed by pressure, stress or heat to another kind of rock. For example, shale, a sedimentary rock of clay particles, can be changed by heat and pressure in to hard metamorphic slate. Marble for example is a metamorphic rock."},{"value":"Methane","id":"417","desc":"The lightest hydrocarbon gas with a chemical formula CH4 and is the chief or predominant component of natural gas."},{"value":"Mesozoic era","id":"418","desc":"It is a geological time scale representing an era between 230 to 65 million years consisting of three distinct periods Triassic, Jurassic and Cretaceous. Generally considered to be an era of dinosaurs and early mammals."},{"value":"Micro log","id":"419","desc":"A logging tool with a spring device and pad. While the spring device holds the pad strongly against the formation, the electrodes in the pad measures the formation characteristics. Micro log is a trade name."},{"value":"Micro caliper log","id":"420","desc":"A caliper log combined with micro log."},{"value":"Micro spherically focused log (MSFL)","id":"421","desc":"The resistivity measurements in a well are taken by a combination of resistivity measuring tool. This is the trade name of a tool, which is run to measure the resistivity of the invaded zone."},{"value":"Migration","id":"422","desc":"The movement of oil from the source rock where it was formed until it is trapped by a trap (a cap rock or a fault or an anticline) to accumulate and form a reservoir."},{"value":"Milled tooth bit","id":"423","desc":"It is a roller cone bit in which each cone is fitted with rows of steel "},{"value":"Milli Darcy","id":"424","desc":"It is a measure of permeability. See darcy. It is equivalent to 0.001 darcy."},{"value":"Minimum tensile strength","id":"425","desc":"It is a specific value for a type of drill pipe or casing at which the pipe will either snap or pull apart"},{"value":"Minimum yield strength","id":"426","desc":" It is a specific value for a type of drill pipe or casing at which the pipe will become permanently distorted."},{"value":"Mist drilling","id":"427","desc":"See foam drilling."},{"value":"Mobile offshore drilling unit (MODU)","id":"428","desc":"See jack up rig."},{"value":"Monel drill collars","id":"429","desc":"Normal steel drill collars can become strongly magnetized that it creates lot of disturbance causing errors in magnetic compasses. Monel drill collars are non-magnetic. They are run as part of the drill string such that the distance between the survey equ"},{"value":"Monkey board","id":"430","desc":"Derrick man?s platform on the derrick. Based on the design of the rig, the monkey board may be at a double or tripe or fourble?s length from the rig floor. The monkey board serves as a platform for the derrick man to stand and handle the pipes during trip"},{"value":"Monobore completions","id":"431","desc":"A completion such that the completed interval is accessible to its full bore by wireline or coiled tubing or any other well intervention tools. Slim hole wells are popular for Monobore completions."},{"value":"Montmorillonite","id":"432","desc":"It is one of the five clay mineral groups. The group is also called fuller?s earth group or smectite group. They are formed by alteration of basic rocks or other silicates low in K under alkaline conditions in the presence of calcium and magnesium. Montmo"},{"value":"Mouse hole connection","id":"433","desc":"This is generally used in only swivel and Kelly based rigs. Top drive rigs generally do not use the mouse hole connections. In drilling mode, when a joint of drill pipe needs to be added to the active drill string, the mouse hole connection is made. The j"},{"value":"Mud","id":"434","desc":"Drilling fluid is one of the most critical components required for drilling a well. It has got several functions but the primary functions of a drilling fluid are to lift cuttings of the wellbore to surface so that the hole is cleaned properly, to exert a"},{"value":"Mud additive","id":"435","desc":"A chemical or material added to the drilling mud to change or maintain or modify certain properties of the mud."},{"value":"Mud balance","id":"436","desc":"A balance used to determine the density of mud in specific units. One end of the balance has a cup to hold mud with a graduated (in specific units) arm with a sliding weight resting on a fulcrum."},{"value":"Mud cake","id":"437","desc":"See filter cake."},{"value":"Mud circulation","id":"438","desc":"See circulating system."},{"value":"Mud cleaners","id":"439","desc":"They are part of the solids control system on a rig and are used to effectively remove fine drilled solids from weighted muds without excess loss barite and fluid. They use a combination of desilters (desilting hydro clones ? see desilters) and a very fin"},{"value":"Mud column","id":"440","desc":"The column of drilling mud filled in the well bore"},{"value":"Mud conditioning","id":"441","desc":"Drilling mud is continuously treated to ensure that the designed and planned properties are maintained. The treatment is called conditioning which may include adding additives, removal of sand and other solids, removal of entrained gas, circulate and cond"},{"value":"Mud flow indicator","id":"442","desc":"A device, which monitors the volume or flow rate of the return mud consistently. If the flow of mud is not constant and is increasing or decreasing, some problem in the well might have occurred. An increase indicates a possible kick and a decrease indicat"},{"value":"Mud-gas separator","id":"443","desc":"A devise that removes the entrained gas from mud at atmospheric pressure. It is normally a tall unit with adequate diameter with a minimum of 8? outlet on top and a 10 feet mud seal at the bottom. The mud with entrained gas is fed from the side on the top"},{"value":"Mud logging","id":"444","desc":"The collection of cuttings brought up by the mud to surface, analysis of the cuttings and recording of information including the detection of hydrocarbon presence and gas analysis is mud logging. In addition, mud logging unit also monitors and records dri"},{"value":"Mud pit","id":"445","desc":"See mud tanks."},{"value":"Mud pumps","id":"446","desc":"A large high pressure single acting triplex reciprocating pump that is used to circulate mud in the well at high pressure and required flow rate. Sometimes double acting two cylinder pumps are also used. Mud pumps come with different horse power rating bu"},{"value":"Mud tanks","id":"447","desc":"A series of open tanks to mix, store and recycle drilling mud. Generally 3 or 4 or more tanks are provided on the rigs. The tanks are divided in to shaker tanks, active tanks and reserve tanks. Mud from active tanks is used for circulation in the well. Re"},{"value":"Mud weight","id":"448","desc":"The density of the drilling mud. Its unit is weight per unit volume. It is usually represented by pounds per gallon (ppg) or pounds per cubic foot or kilograms per cubic meter."},{"value":"Multilateral wells","id":"449","desc":"In a single well bore (main bore or mother bore), two or more horizontal or near horizontal laterals are drilled across the reservoir section and all of them connected to the same main bore to enhance the production and recovery volume. "},{"value":"Multishot survey","id":"450","desc":"It is a directional survey that records the deviation and direction of the well at various points or depths in the hole. Magnetic multi-shot or gyro survey are examples."},{"value":"Multistage cementing","id":"451","desc":"If the cement column is too long in a primary cementing program for casing (mostly happens in an intermediate casing), it may be necessary to cement using multistage cementing process especially if the formation is suspected to be weaker to withstand a la"},{"value":"Multizone completions","id":"452","desc":"It refers to running more than one completion or production string in a well. Common types are dual completion (see dual completion) where two production strings are run in the hole such that production from two different reservoirs can be accomplished wi"},{"value":"Natural gamma ray spectrometry log","id":"453","desc":"It is used to measure and record the relative amounts of radioactive uranium, thorium and potassium in the formation. As the total gamma ray measured from a standard gamma ray log can be misleading as uranium is present both in shales and reservoir rock, "},{"value":"Natural gas","id":"454","desc":"The term is generally associated with gas produced from subsurface as associated gas from an oil reservoir or as non-associated gas from a gas reservoir. It is a light, highly compressible, inflammable mixture of hydrocarbons with varying quantities (in v"},{"value":"Natural rubber element","id":"455","desc":"The packing element of an annular BOP is made of elastomers (rubber) to which steel segments are vulcanized to reinforce and limit the extrusion of rubber when it is activated. Natural is one type of elastomer used suitable for water based muds for temper"},{"value":"Neat cement","id":"456","desc":"Cement with no additives other than water."},{"value":"Neoprene rubber element","id":"457","desc":"The packing element of an annular BOP is made of elastomers (rubber) to which steel segments are vulcanized to reinforce and limit the extrusion of rubber when it is activated. Neoprene is one type of elastomer used suitable for oil based muds for tempera"},{"value":"Neutron log","id":"458","desc":"Neutron long is useful to determine the porosity of the formations."},{"value":"Newtonian fluids","id":"459","desc":"Newtonian fluids show the behaviour whereby the shear stress is directionally proportional to shear rate. These terms are normally used in drilling mud applications and the fluid behaviour model is used to estimate friction pressures, swab and surge press"},{"value":"Nipple up","id":"460","desc":"In drilling, the term generally refers to nippling up or rigging up wellheads and blow out preventer stack."},{"value":"Nitrile rubber element","id":"461","desc":"The packing element of an annular BOP is made of elastomers (rubber) to which steel segments are vulcanised to reinforce and limit the extrusion of rubber when it is activated. Nitrile is one type of elastomer used suitable for oil based or oil additive m"},{"value":"Non-associated gas","id":"462","desc":"A gas that exists as gas at the reservoir that is not associated with oil or which does not come out of solution from oil."},{"value":"Nondispersed mud","id":"463","desc":"A nondispersed mud does not allow or minimises hydration and dispersion of drilled clays by using polymers that encapsulate the clay as quickly as possible avoiding access for the clay to water."},{"value":"Nonporous","id":"464","desc":"A rock that contains no pores or interstices"},{"value":"Normal pore pressure","id":"465","desc":"This refers to pressure of a formation fluid that is normal, i.e. the hydrostatic head of the water gradient specific to the area. The formation fluid may be gas or oil or water but the pressure of the fluid will be equivalent to the normal pressure i.e. "},{"value":"Normal pressure gradient","id":"466","desc":"It is normal pore pressure expressed in terms of pressure per unit length. Its unit is generally psi\/ft. or kPA\/m (kPA = kilo Pascal). This gradient varies from area to area but generally considered to be around 0.465 psi\/foot. Fresh water is 0.433 psi\/"},{"value":"Nozzle","id":"467","desc":"Nozzles are jets fitted to a drilling bit at designed configuration and sizes. As the nozzle?s length as well as inside diameter is very small, it causes the drilling fluid to pass through the bit at high velocity (jet velocity) and designed pressure drop"},{"value":"Oil base mud","id":"468","desc":"A drilling mud in which oil is the continuous phase and contains between 2% to 5% water. Oil based muds have lot of advantages over water based muds ? some of them are increased bore hole stability, prevents hydration and dispersion of clays, near gauge w"},{"value":"Oil emulsion mud","id":"469","desc":"A water base mud in which water is the continuous phase and oil is the dispersed phase"},{"value":"Oil sand","id":"470","desc":"The formation or reservoir that contains oil. Sometimes referred to any reservoir rock that contains oil."},{"value":"Oil saturation","id":"471","desc":"The level or degree of oil saturation in a formation expressed as a percentage of pore volume. Thus the oil saturation is defined as the ratio of the volume of the oil in a porous rock to the pore volume of the same rock. It is expressed in fraction or in"},{"value":"Oil shale","id":"472","desc":"An oil shale that contains oil. However, this oil is not free oil and hence cannot be produced by normal oil well. They are thought to be formed in a special kind of anaerobic environment and are not uncommon to be found in association with coal bearing s"},{"value":"Oil water contact","id":"473","desc":"A well-defined boundary or surface that separates bodies of different lithologies or rock types. Oil water contact is defined as the boundary above, which oil occurs predominantly and below which water occurs predominantly."},{"value":"Oil window","id":"474","desc":"The conditions of time, temperature and pressure in the rocks under which petroleum will form."},{"value":"Oil zone","id":"475","desc":"A strata or formation or horizon of a well in which oil is present. The oil may have a gas cap on top and water at the bottom or it can exist only as oil without gas and water."},{"value":"Offset wells data","id":"476","desc":"Offset wells are existing wells that are in the proximity of the well that is to be drilled and are relevant to the well. Offset wells data are used to evaluate, interpret, understand subsurface lithology and characteristics, achieve regional correlation,"},{"value":"Offshore drilling","id":"477","desc":"Drilling for wells in offshore in shallow or deep water using offshore rigs"},{"value":"Offshore drilling rigs","id":"478","desc":"Offshore drilling rigs are used to drill oil or gas wells in water. There are different types depending upon the water depth and design criteria. Most common are jack-up rigs (mat supported or independent leg) that are used generally up to 120 m of water "},{"value":"Openhole completion","id":"479","desc":"The open hole across the pay zone (producing reservoir) is kept open without running a casing. The well is produced directly from the reservoir as barefoot completion or by placing a pre-drilled casing across the reservoir to prevent hole caving in or by "},{"value":"Onshore drilling","id":"480","desc":"Drilling for wells on land using land rigs."},{"value":"Onshore drilling rigs","id":"481","desc":"Designed for drilling oil and gas wells on land. They are of different types and models depending upon the terrain and design criteria. Some common types are mobile land rigs (usually for shallow depths below 3,000 m ? some may be capable of more also), d"},{"value":"OPEC","id":"482","desc":"Organization of Petroleum Exporting Countries. It was formed in September 1960 in Baghdad and it currently has 12 members - Venezuela, Saudi Arabia, Iran, Iraq, Kuwait, Algeria, Angola, Ecuador,Libya, Nigeria, Qatar and UAE. OPEC controls the policy of o"},{"value":"Organic rock","id":"483","desc":"The materials inside the rock are made of plant or animal life. Organic rocks are good source of petroleum."},{"value":"Organic theory","id":"484","desc":"It is one of the but most accepted theory of origin of petroleum that is based on the accumulation of hydrocarbons from living things and that the hydrocarbons are generated by the action of heat at the appropriate pressure on biogenically formed organic "},{"value":"Overbalanced drilling","id":"485","desc":"Overbalance refers to the excess of the mud hydrostatic pressure against the formation pore pressure. Overbalance drilling refers to drill the well with the overbalance (i.e. mud hydrostatic pressure is kept higher than the formation pressure)."},{"value":"Overburden","id":"486","desc":"The overlying rock above the point or depth of interest."},{"value":"Overburden pressure","id":"487","desc":"The stress or pressure exerted by the overlying rock or sediments above a depth or formation of interest. It is usually considered to be about 1.0 psi\/ft although the value can vary depending on a specific area. Hence this value can be considered for appr"},{"value":"Overburden stress","id":"488","desc":"See overburden pressure"},{"value":"Overshot","id":"489","desc":"One of the most commonly used fishing tools for fishing out pipes. It has a grapple (either basket or spiral) that firmly grips the pipe and catches the fish. It is normally run on drill pipe with other fishing equipment like jars, bumper sub and safety j"},{"value":"Overthrust belt","id":"490","desc":"It refers to an area or region in the earth?s crust, which is characterized by overthrust faulting."},{"value":"Overthrust fault","id":"491","desc":"It is a reverse fault (angle of the fault plane is low from the horizontal) where a large displacement, usually in miles, has occurred. Thrust faults are often recognized by older (aged) rocks being found above much younger rocks."},{"value":"Packed Bottom Hole Assembly","id":"492","desc":"While drilling a well, the packed hole assembly is used to maintain the drift angle and direction of a hole. The packed hole assembly generally consists of stabilizers (see Stabilizers) and drill collars arranged in a particular fashion. The assembly is o"},{"value":"Packer","id":"493","desc":"An integral part of the completion string used for production or with test string for testing. A packer is a device that seals the tubing to casing annulus and forces the produced fluid from the wellbore in to the completion tubing. The packer has slips t"},{"value":"Packer Fluids","id":"494","desc":"The packer fluid is placed above the packer in the annulus between tubing and casing. The primary purposes of a packer fluid are to control the formation pressure and to minimize the differential pressure across the packer. At the same time when it comes "},{"value":"Pay Zone","id":"495","desc":"The formation or zone from where hydrocarbons are produced. It may be sandstone or limestone or fractured granite or any other formation as long as it produces hydrocarbons. Also called as producing zone."},{"value":"PDC Bit","id":"496","desc":"An abbreviation for Poly-Crystalline Diamond Compact Bit. Unlike roller cone bits that have three independently moving cones (see roller cone bits), PDC bits have a fixed head that rotates as one piece with the drill string. It is a shear bit that cuts th"},{"value":"Pendulum Assembly","id":"497","desc":"While drilling a well, a pendulum assembly is used to decrease or drop the drift angle. It works on a pendulum on the principle of pendulum effect. "},{"value":"Pendulum Effect","id":"498","desc":"It is used to drop the drift angle in a well by using a pendulum assembly, which has a tendency to hang in a vertical position, and by controlling the weight on bit and rotary speed, the drop of angle can be achieved. For the effect to take place properly"},{"value":"Penetration Rate","id":"499","desc":"It refers to rate of drilling in length per unit time. Its unit is normally ft\/hr or m\/hr."},{"value":"Perforation","id":"500","desc":"Perforations are holes generally made in a cemented cased hole. The primary purpose of perforations is make a conduit for the hydrocarbons to flow from the formation through the cement (between casing and formation) and the casing. Perforations are also m"},{"value":"Perforating Gun","id":"501","desc":"Perforating guns are fitted with charges (explosives) as per the design requirements and are used to make the perforations. Guns are run on wireline as casing guns or on tubing as tubing conveyed perforation (TCP) guns. The shot density can also be varied"},{"value":"Permeability","id":"502","desc":"The formation rocks have pore spaces in which gas or oil or water is filled in. The permeability is a measure of connectivity between pore spaces and the ease with which the fluid flows through the connecting pore spaces of the rock. Permeability is an im"},{"value":"Petroleum","id":"503","desc":"It is a naturally occurring substance in the earth in solid, liquid or gaseous state. It composes mainly of the chemical compounds having carbon and hydrogen but sometimes with elements like sulfur. In some cases, especially in oil industry, petroleum ref"},{"value":"pH or pH Value","id":"504","desc":"It is a unit of measurement that is used as a reference scale to identify the acidity or alkalinity of a liquid. A neutral solution (such as pure water) has a pH of 7, an acid solution has less than 7 and basic or alkaline solutions have more than 7."},{"value":"Pin","id":"505","desc":"It is the shoulder or end of the pipe were male threads are made."},{"value":"Pipe","id":"506","desc":"It is generally a hollow cylinder through which fluids are pumped or carried through. In oil and gas, a pipe refers to drill pipe, casing, tubing, line pipe, etc."},{"value":"Pipe Rack","id":"507","desc":"A Pipe rack is a horizontal support where pipes are racked on a rig."},{"value":"Pipe Tongs","id":"508","desc":"See Tongs."},{"value":"Pit Gain","id":"509","desc":"A gain or increase of level in the mud pits. If the increase is not due to addition of mud from any other tank or chemicals, then the increase may be an indication of a kick."},{"value":"Pit Level","id":"510","desc":"The level or height of drilling mud or brine or any other drilling fluid in the mud tanks (also called as mud pits)."},{"value":"Pit Level Indicator","id":"511","desc":"It is a device used to continuously monitor the pit levels (the level of mud in the pits). The indicator at the pits has a float device and a sensor, which transmits the data continuously to a panel mounted on driller?s console and\/or to the computers of "},{"value":"Plastic Viscosity","id":"512","desc":"Viscosity is a measure of the resistance to flow. Plastic viscosity is a component of viscosity that is caused by mechanical friction within the drilling mud due to interaction between the solids, between solids and liquid and the deformation of liquid, w"},{"value":"Plug and Abandon","id":"513","desc":"To abandon a dry hole (a well that has no oil or gas) with cement plugs"},{"value":"Polymer Muds","id":"514","desc":"A water based drilling mud that uses polymers to increase viscosity (by using viscosifying polymers), filtration control (by using organic polymers). In polymer muds bentonite is added not more than 1 to 2 pounds per barrel only if needed for filtration c"},{"value":"Poor Boy Degasser","id":"515","desc":"See Mud-Gas Separator"},{"value":"Pores","id":"516","desc":"Pores are cavities or spaces within a rock that are usually small and filled with a fluid (it can be gas or oil or water)."},{"value":"Porosity","id":"517","desc":"Porosity is the amount of connected space between the rock grains that can be filled by fluids. It is the ratio of the volume of empty space to the volume of the solid rock in a formation measured as a percentage of the total volume."},{"value":"Porous","id":"518","desc":"A rock is said to be porous if it has pores with fluid in it."},{"value":"Potassium Chloride (KCl)","id":"519","desc":"Potassium chloride is a mud additive that is used to inhibit the hydration and dispersion of hydratble shales. The K+ (potassium ion) is utilized to provide the inhibition. KCl in solution is a very popular brine used for testing and completion purposes."},{"value":"Pounds per Gallon (ppg)","id":"520","desc":"It is a unit of mud density or weight. A 10 ppg mud means that one gallon of mud will weigh 10 pounds. "},{"value":"Power Law Model","id":"521","desc":"See Newtonian Fluids (Note: Power Law Model applies for a Non-Newtonian Fluid like Drilling Mud)."},{"value":"Power Slips","id":"522","desc":"Slips are used to hold the drill string in the rotary table ? for details see Slips. Power slips are pneumatically or hydraulically actuated devices that remove the need for manual handling of slips by the rig crew."},{"value":"Power Tongs","id":"523","desc":"They are mostly used to run casings or tubings using hydraulic power thereby helping the pipes or casings run faster with the appropriate torque."},{"value":"Pre-Cambrian Era","id":"524","desc":"It is a time period in the geological time scale from prior to 570 million years and probably until the formation of earth around 4.3 billion "},{"value":"Pre-Spud Meeting","id":"525","desc":"A pre-spud meeting is an integral part of well planning and preparation process. Before the drilling commences, the pre-spud meeting will be held either on the rig or at the base office to communicate the well objectives\/drilling program and to bring clar"},{"value":"Pressure","id":"526","desc":"Pressure is a force that is exerted uniformly in all directions and all points in a vessel, pipe or wellbore. Its unit is expressed as force per unit area as psi ? pounds per square inch (psi) or KPa? kiloPascals or bar."},{"value":"Pressure Depletion","id":"527","desc":"When hydrocarbons are produced, the reservoir pressure starts declining from the initial reservoir pressure, the rate of decline and commencement of decline depending on various parameters such as rate of draw down, production rate, reservoir type, fluid "},{"value":"Pressure Gradient","id":"528","desc":"In drilling, pressure gradient is the pressure expressed as a gradient in relation to depth. It is expressed as pressure per unit depth. Its common units are psi\/ft. or KPa\/m. It normal terms, it is also expressed as the change in atmospheric pressure alo"},{"value":"Pressure Test","id":"529","desc":"It is mandatory on a rig to test to the required pressure all the high pressure equipment at scheduled intervals. Blow out preventers, kill and choke lines, choke manifold, standpipe manifold, lower and upper kelly cocks etc are some of the critical high "},{"value":"Primary Cementing","id":"530","desc":"The cementing job that is carried out after the casing is run in the hole. The cement provides a bond between the casing and formation thus isolating reservoir zones thereby preventing any undesirable migration of fluids. "},{"value":"Production Casing","id":"531","desc":"The casing that is run across the reservoir sections through which the well will be produced."},{"value":"Production Log","id":"532","desc":"The main purpose of the production log is to determine the contribution of each zone (in case of co-mingled stacked sands or multiple zones) to the total production or injection."},{"value":"Producing Zone","id":"533","desc":"See Pay Zone."},{"value":"Pounds Per Square Inch (psi)","id":"534","desc":"Unit of pressure.10 psi means for every square inch, there will be a pressure equivalent to 10 pounds"},{"value":"Pulling Out of Hole (POOH)","id":"535","desc":"Pulling out of hole means pulling out the bit (to change or at well target depth) or drilling string or tubing or casing or wireline logging tools, etc."},{"value":"Pump","id":"536","desc":"See Mud Pump."},{"value":"Pup Joint","id":"537","desc":"A short drill pipe or drill collar or casing or tubing. They will be shorter than normal length of the pipe. They are mainly used for space out requirements. A short casing may also be used as a marker joint to identify the depth by running a casing colla"},{"value":"Quaternary","id":"538","desc":"It is a period in the geological time scale. It is the second period of the Cenozoic era, following the Tertiary period. Its age is about two million years and it extends to the present. This is the period during which human beings evolved."},{"value":"Quartz Arenite","id":"539","desc":"It is sandstone but contains mostly pure quartz grains and cement."},{"value":"Quartzite","id":"540","desc":"It is a very hard, clean, white metamorphic rock formed from quartz arenite sandstone."},{"value":"Rack","id":"541","desc":"Rack is a framework that supports the stacking or placing of objects such as pipe. When it supports the pipes, it is called pipe rack."},{"value":"Rack Pipe","id":"542","desc":"When drill pipe stands are pulled out of hole, they are racked on the rig floor."},{"value":"","id":"543","desc":"Drill pipes, casings and tubings come in varying lengths. They are generally grouped into three ranges(R1, R2 and R3) defined as:\nR1 ? 5.0 to 7.3 m, R2 ? 7.6 to 10.0 m and R3 ? 10.0 to 13.7 m"},{"value":"Rate of Penetration (ROP)","id":"544","desc":"It is the speed of drilling defined as meters per hour or feet per hour."},{"value":"Rat Hole","id":"545","desc":"Rat hole is a hole in which Kelly and swivel are placed on the rig floor. The rathole has a scabbard into which Kelly will be inserted."},{"value":"Reactive Torque","id":"546","desc":"It is the twisting effect caused by the down hole motor due to its rotation and the bit rotation. This effect tends to move the drill string in the opposite direction to that of the bit. It depends on the physical properties of the motor, length of drill string, formation characteristics, weight on bit etc."},{"value":"Recovery Efficiency","id":"547","desc":"It is the recoverable volume of oil and gas from the total in place volume expressed as a percentage."},{"value":"Recovery Factor","id":"548","desc":"See Recovery Efficiency."},{"value":"Relative Density","id":"549","desc":"There are two definitions ? one for liquids and one for gases. (i) For liquids - It is the ratio of the weight of a given volume of a substance at a given temperature to the weight of an equal volume of water at the same temperature and (ii) For gases - It is the ratio of the weight of a given volume of a gaseous substance at a given temperature to the weight of an equal volume of air at the same temperature."},{"value":"Relative Permeability","id":"550","desc":"When more than one fluid is present in a reservoir rock, the relative permeability is the ratio of effective permeability to absolute permeability. If only one fluid is present in the rock, then the relative permeability will be equal to 1."},{"value":"Reservoir","id":"551","desc":"Reservoir is a porous, permeable and sedimentary rock in which hydrocarbon fluids or water are accumulated. Common reservoir rocks are sandstones and limestones. Apart from these, fractured granite (not a sedimentary rock) is found to contain hydrocarbons. In the typical oil reservoir (that contains gas, oil and water), gas, the lightest, occupies the upper part, oil the middle and water the lower part. If gas is present independently the reservoir is called gas reservoir. In retrograde condensate reservoirs, the gas exists as gas phase in the reservoir conditions but when the pressure drops below the dew point the condensate separates from the gas as liquid phase."},{"value":"Reservoir Drive","id":"552","desc":"See Drive."},{"value":"Reservoir Pressure","id":"553","desc":"See Formation Pressure."},{"value":"Reverse Circulation","id":"554","desc":"In reverse circulation, the drilling mud or brine or any other fluid is pumped downward through the annulus such that the returns to surface are taken through the drill pipe or tubing. This is opposite to that of normal circulation. This is not generally used in open hole but in cased hole it is commonly used for many operations."},{"value":"Rheology","id":"555","desc":"It relates to the flow of gases and liquids but in drilling it is important for drilling muds and cement slurries."},{"value":"Rig Floor","id":"556","desc":"This is the main area on a rig where the drilling activities take place. The legs of the mast stands at each corner of the rig floor. It sits above the substructure on which the draw works, rotary table, dog house, etc are located. It is also called derrick floor."},{"value":"Roller Cone Bit","id":"557","desc":"A drilling bit made of two or three cones that are mounted on special bearings. The surface of each cone is made of rows of steel teeth or rows of tungsten carbide inserts. Also called rock bit. See Bit."},{"value":"Rotary Hose","id":"558","desc":"A steel reinforced, flexible hose that is installed between the standpipe and the swivel or top drive. It carries the drilling mud from the standpipe to the swivel or top drive. It has adequate length to travel along with swivel or top drive when it moves up and down during operations. Also called the Kelly hose or mud hose."},{"value":"ROP","id":"559","desc":"See Rate Of Penetration."},{"value":"Rotary or Rotary Table","id":"560","desc":"It is the machinery used to provide the rotation required to rotate the drill string and the bit for drilling. It is powered either by an independent motor or is coupled with draw works. The Rotary transmits the rotation to the Kelly bushing which in turn turns the Kelly, drill string and the bit. Rotary table is generally used only in Kelly and swivel rig. Top drive rigs may have a rotary table as a back up only."},{"value":"Rotary Drilling","id":"561","desc":"In rotary drilling the drilling is carried out by rotating the bit and by applying weight on it. The bit is made up to the drill string that also serves as a passage for drilling fluid for circulation. The drill string is rotated through a Kelly by the rotary table."},{"value":"Rotating Head","id":"562","desc":"It is a type of annular BOP that can seal off the annular space between the drill pipe or Kelly while allowing drilling to continue. It is used for special applications like managed pressure cap drilling where formation gas is allowed to flow continuously while drilling. The rotating head seals off the annulus such that the gas is diverted away from the rig thereby protecting the rig and surface equipment."},{"value":"Rotary Shouldered Connection","id":"563","desc":"The joints (drill pipe, drill collars etc) that are used in rotary drilling have connections made at the shoulders (pin and box) and hence called as rotary shouldered connection."},{"value":"Rotary Speed","id":"564","desc":"The speed of the rotary table measured in revolutions per minute, indicated as RPM."},{"value":"Rotary Torque","id":"565","desc":"The torque applied to the drill string due to rotation."},{"value":"Reverse Fault","id":"566","desc":"A dip-slip fault along which the hanging wall has moved upward relative to the footwall. Also called a thrust fault."},{"value":"Rift Zone","id":"567","desc":"The zone along which crustal plates separate because of slowly diverging convection currents in the semisolid, deformable mantle. As the rift widens and the landmasses on both sides move apart, new oceanic crust is formed. Since the Mid-Atlantic rift zone opened about 200 million years ago, North and South America have been moving away from Europe and Africa at a rate of 114 inches a year."},{"value":"Rollover Anticline","id":"568","desc":"An anticline formed when the dip of a growth fault approaches the horizontal at depth and deposition is faster on the downthrown side, which tends to \"roll over\" or curl downward."},{"value":"Rollover Fault","id":"569","desc":"See Growth Fault."},{"value":"Safety Joint","id":"570","desc":"It is part of the fishing string run to catch and retrieve a fish from a well. If the fish does not get released, then the fishing tool must be disengaged from the fish so that some other fishing string can be run to free the fish. If the fishing tools do not get disengaged, then the safety joint allows easy disengagement. In that case, a part of the safety joint and the fishing tool will be left in the hole as part of the fish. However, the string would be pulled out safely to run another string to retrieve the fish."},{"value":"Salt Dome","id":"571","desc":"An intrusion of salt due to the relative buoyancy of salt when buried beneath other types of sediments, which forms a dome by rupturing the overlaying rock sometimes developing a narrow neck at bottom giving it a balloon like structure. The formations above the salt dome are usually arched so that they dip in all directions away from the center of the dome, thus frequently forming traps for petroleum accumulations."},{"value":"Salinity","id":"572","desc":"It is a measure of the amount of salt dissolved in a liquid and in drilling it measures the amount of salt in drilling mud or brine. Usually represented as ppm (parts per million)."},{"value":"Sandstone","id":"573","desc":"A detrital sedimentary rock (in the group of arenaceous rocks) in which the particles or grains range in size from 1\/16 mm to 2 mm in diameter. Most sandstones are dominated by quartz, feldspar and rock fragments bound together by a cement of silica, carbonate or other minerals or a matrix of clay minerals. Sandstone is porous and permeable and hence makes a good reservoir to accumulate producible hydrocarbons."},{"value":"Sand Production","id":"574","desc":"The production of sand along with the flow of reservoir fluids. Sand production is undesirable as it can erode completion equipment, surface facility equipment, reduce the productivity, block the completion tubing thereby refusing access of downhole tools to the perforations. Hence sand control is essential in formations that are not competent to hold the sands intact."},{"value":"Saturation","id":"575","desc":"Generally means the relative amount of oil, gas and water in the reservoir rock. It is denoted usually by percentage of volume. Saturation of oil is an important data to determine the in-place volume of oil in the reservoir."},{"value":"Saver Sub","id":"576","desc":"It is generally referred to a sub that is used between the Kelly and the drill pipes. As kelly is used several times to make connections and as it is a very expensive item, the threads of the kelly cannot be allowed to get damage due to frequent connections. Hence a small sub is used at the bottom of the Kelly and it is used to frequently to make connections of the drill pipe."},{"value":"Scraper","id":"577","desc":"It is a device used to run on drill pipe or tubing to scrap the walls of the casings to remove any scale or deposits or even cement before a packer is run. Scraper also is a device used to remove the deposits of scale or paraffin wax from pipelines, flow lines, tubings etc."},{"value":"Seamless Drill Pipe","id":"578","desc":"Drill pipes that are seamless and in one continuous piece that means no joints or welding."},{"value":"Set Back","id":"579","desc":"Set back is referred to placing of drill pipe and drill collar stands in one side of the rig floor sufficiently away from rotary table. "},{"value":"Secondary Migration","id":"580","desc":"Secondary migration is considered to be the movement of generated hydrocarbons from the source rock through carrier beds to reservoir rocks leading to oil and gas accumulations."},{"value":"Secondary Recovery","id":"581","desc":"The second stage of hydrocarbon recovery. Water or gas is injected into the reservoir to maintain the reservoir pressure and to support the displacement of hydrocarbons into the wellbore."},{"value":"Sediments","id":"582","desc":"Organic or inorganic solid fragmental matter which originates from weathering of rocks and transported and deposited by air, water or ice or that is accumulated by chemical precipitation from solution or secretion from organisms. When deposited, it generally formslayers of loose, unconsolidated materials such as sand, gravel, silt, mud, till, loess, alluvium."},{"value":"Sedimentary Basin","id":"583","desc":"A depression or basin where various sediments are allowed to settle from a transporting medium like river water and accumulate. They can vary from bowl shaped to elongated troughs."},{"value":"Sedimentary Rock","id":"584","desc":"Sandstone, shale or limestone is sedimentary rock."},{"value":"Seismic Survey","id":"585","desc":"A geophysical exploration method in which sound waves (acoustic) generated from a source (dynamites or vibrators) that travel to the subsurface underground. The sound waves travel through the layers of the earth's crust and at formation bound?aries some of the waves are reflected back to the surface where sensitive detectors called geophones pick and record them. The data thus recorded is then converted or processed to develop readable seismic data, which is then used to interpret and evaluate to look for hydrocarbon bearing zones."},{"value":"Semi-Submersible Drilling Rig","id":"586","desc":"It is a type of offshore rig that floats during drilling supported by large pontoons submerged in water. The deck is connected and supported by large diameter buoyant columns at the corners and small intermediate columns that are connected to the pontoons. Most of the semi-submersibles are not self-propelled and hence have to be towed. The anchored or moored semi-submersibles can drill in water depths up to 1,500 m and dynamic positioning semi-submersibles can drill beyond 3,000 m water depth."},{"value":"Shale","id":"587","desc":"A fine grained detrital sedimentary rock composed mostly of consolidated clay, silt or mud. Its color may be red, brown, black or grey. A highly compacted impermeable shale can act as a cap rock to trap oil migration."},{"value":"Shale Oil","id":"588","desc":"See Oil Shale."},{"value":"Shale Shakers","id":"589","desc":"It is the most important equipment in the rig?s solid control system to remove drill cuttings from the mud. It is a vibrating equipment that has a set of screens (mesh screen). The mud from the well along with the drill cuttings flows over the screensas they vibrate. The mud and the solids that are smaller than the mesh size of the screen pass through the screen for further treatment and re-use while the larger solids fall off from the edge of the screen and are separated from the mud stream."},{"value":"Shallow Gas","id":"590","desc":"It is mostly natural gas accumulation that is located at a shallow depth from the surface. It is potentially dangerous while drilling because if encountered it can only be diverted from the wellbore and not controlled. Also as the timing for the crew?s reaction to act is very low due to its shallow depth that sometimes before the diversion equipment is activated, the gas can flow to the surface and the rig floor causing a high potential risk."},{"value":"Shear Ram","id":"591","desc":"It is the component of a blow out preventer that is used to shut the well by shearing the pipe. This is only done in an emergency in case there is no time to pull the pipe or the pipe rams or annular BOP are not operational in a kick situation."},{"value":"Shut In Pressure","id":"592","desc":"It is the pressure noted at the surface when the well is shut in by the Blowout Preventers (BOPs), X-Mas Tree or Production Manifold either during a kick situation or during a test or during production."},{"value":"Shut In Bottomhole Pressure","id":"593","desc":"It is the pressure exerted at the bottom of a wellbore when the well is shut in either during a kick situation or during a test or during a production. The well can be shut in at the surface or down below if a down hole shut in valve is present (usually run during testing a well). If the well is shut-in at the surface, the bottomhole pressure is the sum of hydrostatic pressure exerted by the fluid column and any additional applied pressure."},{"value":"SICP","id":"594","desc":"Shut in casing pressure. It is the annular (between drill pipe and casing) pressure at the surface at the surface when the well is shut in by the blow out preventers during a kick situation. It is equal to the formation pressure minus the hydrostatic pressure in the annulus (consisting of mud plus the formation fluid that has entered the wellbore during the kick). Usually the SICP is higher than the SIDPP due to the presence of lighter fluid in the annulus."},{"value":"SIDPP","id":"595","desc":"Shut in drill pipe pressure. It is the drill pipe pressure at the surface when the well is shut in by the blow out preventers during a kick situation. It is equal to the formation pressure minus the mud hydrostatic pressure inside the drill pipe."},{"value":"Side Tracking","id":"596","desc":"It is to drill another wellbore sidetracking from the original wellbore. The sidetracking can happen for mainly two reasons ? (i) for geological reasons example to explore or appraise the structure in an updip or downdip position and (ii) due to an unrecoverable fish left in the hole as in this case drilling cannot continue in the same wellbore."},{"value":"Sidewall Core","id":"597","desc":"It is a core taken from the walls of the wellbore usually by a wireline tool. The tool has hollow bullets that are fired in to the wall of the wellbore. The hollow bullets catch the core and they are retrieved with the tool. At a time up to 30 bullets can be run in a tool."},{"value":"Silicate Muds","id":"598","desc":"It is a water based inhibitive mud using sodium or potassium silicate as the inhibiting chemical."},{"value":"Siltstone","id":"599","desc":"A fine-grained sedimentary rock composed mostly of particles 1\/16to 1\/256millimeter in diameter with texture intermediate between sandstone and shale."},{"value":"Slate","id":"600","desc":"It is a metamorphic rock formed when shale is buried deeply due to the heat and pressure and resulting fusion of mineral grains in to slate."},{"value":"Slant Rig","id":"601","desc":"A specially designed rig that is used for drilling directional wells. As the rig is slant, the drilling can commence at the slant angle directly."},{"value":"Slick Drill Collar","id":"602","desc":"For definition see Drill Collar. Drill collars are of two types ? Slick or Spiral. For spiral, see spiral groove drill collar. Slick drill collars have a plain outer surface with no grooves. Nowadays mostly spiral groove drill collars are used for drilling."},{"value":"Sliding Sleeve","id":"603","desc":"It is a completion jewellery and a part of the completion tubing. It is used to allow circulation or communication between the tubing and the annulus above the packer as required."},{"value":"Slickline","id":"604","desc":"It is a thin steel wire run on a slickline unit to place or retrieve hardware like plugs, gauges or valves in a completion string. It is also used to run shifting tools to operate (open and close) the sliding sleeves."},{"value":"Slips","id":"605","desc":"They are used to hold the pipe at the rotary table. The slip is a wedge shaped solid piece of metal with gripping elements stacked inside. The slip wedges against the master bushing of the rotary table while the gripping elements grip the pipe and prevents it from slipping down in to the hole. Slips are specific for the type and size of pipe used - drill pipe slips, drill collar slips, casing slips, tubing slips etc."},{"value":"Slip Velocity","id":"606","desc":"The cuttings generated while drilling is lifted by the circulating mud from the bottom to the surface. However, depending upon the density and size of the cuttings, they are pulled down by gravity through the mud and the velocity of the cuttings that fall through the mud is called slip velocity. For cuttings to be removed from the hole, then the mud annular velocity must be higher than the slip velocity."},{"value":"Sloughing","id":"607","desc":"Reactive shale in a well gets absorbed by water, swells, sloughs off and falls into the well bore."},{"value":"Snubbing Unit","id":"608","desc":"If the bit is close to the surface and the well becomes active and the bit cannot be run back to bottom even by stripping (see stripping), then a snubbing unit is used to run the pipe back in the hole to bottom in a live well by means of specialized handling and sealing systems."},{"value":"Solution Gas","id":"609","desc":"Gas that exists in solution in oil but gets released as gas from the solution during production when the pressure reaches the bubble point."},{"value":"Solution-Gas Drive","id":"610","desc":"A type of drive that forces the movement of oil through a reservoir and the wellbore. The gas that exists in solution expands when it comes out of solution. The expansion provides the energy to force the oil to move."},{"value":"Sonic Log or Sonic Logging or Acoustic Logging","id":"611","desc":"An electric log that helps to record the acoustic characteristics of subsurface formations based on the travel time for sound waves through the rock. The rate of travel depends on the composition, porosity and fluid content."},{"value":"Source Rock","id":"612","desc":"It may be defined as a fine grained sediment that in its natural setting has generated from organic materials and released enough hydrocarbons to form commercial accumulation of hydrocarbons."},{"value":"Sour Crude or Sour Crude Oil","id":"613","desc":"Oil that contains hydrogen sulfide or other acid gas."},{"value":"Sour Gas","id":"614","desc":"In drilling hydrogen sulfide and carbon-di oxide are considered as sour gas."},{"value":"Spear","id":"615","desc":"It is a fishing tool that is used to retrieve a fallen pipe (especially casing). Spear catches the fish from the inside of the pipe against the overshot which catches the fish on the outside."},{"value":"Spill Point","id":"616","desc":"The structurally lowest point to which a reservoir can trap and retain hydrocarbons. Beyond the spill point, the hydrocarbons spill or leak and continue to migrate to get trapped elsewhere."},{"value":"Spinning Wrench or Spinners","id":"617","desc":"They are used to spin the drill pipes in making connections prior to applying the final torque with the tongs and in breaking connections after the connection is broken by applying the required torque by the tongs. Spinners are not used for applying final torque. Spinners can be either air-powered or hydraulically powered. Some spinners called iron roughnecks can also provide the final torque."},{"value":"Spiral Groove Drill Collar","id":"618","desc":"For definition see drill collar. Drill collars are of two types ? slick or spiral. The spiral drill collars have a long continuous groove machined in the outer surface. The spiral groove helps to minimize the contact area between the collar and the wall of the open hole thus minimizing the differential sticking."},{"value":"Spontaneous Potential Log","id":"619","desc":"It is an electric log that is used to record the electrical voltages of the formation. It is used to differentiate permeable zones from non-permeable sections like sand from shale."},{"value":"Squeeze","id":"620","desc":"A careful injection of a treatment fluid under pressure to treat a zone or formation. A squeeze is also used to inject cement slurry under pressure through perforated casing for a remedial job to isolate a particular formation or to improve the quality of cement bond behind the casing."},{"value":"Stabilizer","id":"621","desc":"They are a part of the drill string used to maintain the angle of the well or to build or drop the angle. They are run in a particular fashion in combination with drill collars above the bit to achieve a specific objective ? i.e. to maintain or build or drop the angle by controlling the location of the contact point between the hole and the collars."},{"value":"Stand","id":"622","desc":"A stand is generally referred to 3 joints of drill pipe joined together. A stand of 3 drill pipes is around 27 to 28.5 m and is racked back in the derrick during a trip. Sometimes a stand of 2 joints is also used if the rig height is designed to accommodate only a 2 joint stand."},{"value":"Stimulation","id":"623","desc":"It is a process used to improve the Productivity or Injectivity of a formation. Examples are acidizing or hydraulic fracturing."},{"value":"Stratigraphy","id":"624","desc":"A branch of geology or science that studies the origin, deposition, classification, description, composition, distribution of rock strata."},{"value":"Strata","id":"625","desc":"Distinct, usually parallel, layers of sedimentary rocks that form beds (originally horizontal). It is plural for stratum as an individual bed is a stratum."},{"value":"Stratigraphic Trap","id":"626","desc":"A geological structure formed by changes in rock type or pinch outs or unconformities or reefs that are capable of trapping and retaining hydrocarbons. "},{"value":"Stripping","id":"627","desc":"While tripping out of the hole (pulling out of the hole), if the well becomes active (a kick had occurred), then it is critical that the bit is run back to back as close to bottom as possible so that the well can be killed by conventional methods and more comfortably. However, it may not be possible to run bit as normal running in hole with the well being active. Hence the method of stripping is used. Stripping is done by running the pipe with the annular BOP closed. The annular BOP closing pressure is adjusted such that when the pipe is run in hole it allows the displacement of pipe metal volume while at the same time permits maintaining a constant bottom hole pressure. Sometimes instead of the annular BOP, a set of two pipe rams is used for stripping."},{"value":"Steerable Motor","id":"628","desc":"A mud motor with bent housing that is run above the bit. The motor can be used to steer the wellbore in directional drilling applications. The motor is flexible in the sense that it builds angle in sliding mode (no drill string rotation) and allows drilling ahead in rotary mode (with the drill string rotation)."},{"value":"Stock Tank Barrel","id":"629","desc":"It is a measure of the oil stored in storage tanks. It is denoted by the abbreviation STB."},{"value":"Stratigraphic Unit","id":"630","desc":"A stratum or strata considered as aunit in the classification of the rocks for any purpose such as Description, Mapping and Correlation."},{"value":"Strike","id":"631","desc":"The Azimuth or direction at the intersection of a plane with a horizontal surface."},{"value":"Structural Trap","id":"632","desc":"A type of geological structure that is capable of trapping and retaining hydrocarbons. Examples are faults or folds."},{"value":"Stuck Pipe","id":"633","desc":"When the drill string or casing or tubing becomes stuck in the hole such that it cannot be moved is called stuck pipe. Sticking occurs while drilling or tripping or running casing. Stuck pipe may be mechanical or differential. Mechanical stuck pipe is when the hole collapses around the pipe or an object is obstructing the movement. Differential sticking occurs when the hydrostatic head of the mud is sufficiently higher than that of a permeable formation (example sand) in combination with thick filter cake and high contact area between the drill collars and the wall of the open hole (see differential sticking)."},{"value":"Sub","id":"634","desc":"See Crossover Sub and Saver Sub."},{"value":"Subnormal Pressure","id":"635","desc":"A formation pressure that is less than the normal pressure of a formation. See Normal Pressure."},{"value":"Subsurface Safety Valve (SSSV)","id":"636","desc":"It is a safety valve installed on the completion string such that the valve is closer to the surface. The valve will shut off the production well in case of an emergency at the surface installations. The valve is controlled hydraulically."},{"value":"Surging Effect","id":"637","desc":"It happens when a bit or casing is running into the hole. If the bit and stabilisers or casing are run in too fast and if the mud is viscous, then the mud below the bit or casing cannot travel up at the same speed to displace an equivalent volume of steel that is being run thereby temporarily creating a pressure surge to the formation below. This causes a surge effect temporarily but that may be adequate sometimes to induce losses in the well."},{"value":"Surfactant","id":"638","desc":"Surfactants mean surface-active agents and they are used to reduce the interfacial tension between two phases (oil and water for example). Oil and water cannot form a stable system on their own as they always tend to identify as two independent phases. A surfactant introduced to an oil-water system can stabilize the system. Surfactants are used in the petroleum industry as additives to drilling mud and to water during chemical flooding. Also called wetting agents or emulsifiers."},{"value":"Swabbing Effect","id":"639","desc":"It happens when a bit is pulled put of hole. If the bit and stabilisers are balled up, mud is viscous and the bit is pulled too fast, then the mud above the bit cannot fill up at the same speed the space created by the movement of the bit upwards thereby temporarily creating a reduction in hydrostatic head. This causes a suction effect temporarily but that may be adequate for the formation fluids to enter the wellbore (a kick). In production operations, swabbing refers to swab the well to activate the flow of hydrocarbons from the reservoir rocks."},{"value":"Sweet Crude Oil","id":"640","desc":"An oil that has no hydrogen sulfide and carbon-di oxide."},{"value":"Swivel","id":"641","desc":"The Swivel is one of many engineering marvels that has three important functions ? to suspend the drill string while drilling while at the same time to allow or permit free rotary motion to the string and be a passage way for drilling mud to circulate from the mud pump to the drill string. Top drive rigs do not use swivel as top drive does all the functions of the swivel as well as rotary table."},{"value":"Synthetic Based Mud","id":"642","desc":"Synthetic based muds were developed to replace oil muds so that the environmental issues that arise out of using oil based mud can be prevented. Synthetic based muds serve the purpose closely to that of oil based mud and are widely used."},{"value":"Tally","id":"643","desc":"It is the record of individual and the total (cumulative) length of pipe or tubing or casing that is run in to the hole."},{"value":"Tapered string","id":"644","desc":"The various components of the drill string reduce in size as the string goes up in the hole ? for example a drill string can consist of ? from bottom ? bit ? 8? drill collars ? 6.1\/2? drill collars ? 5? drill pipe at the top."},{"value":"Temperature gradient","id":"645","desc":"Defined as the rate of change of temperature as the depth of the well increases. Denoted by temperature per unit length. Commonly used units are 0F per 100 feet or 0C per m."},{"value":"Temperature log","id":"646","desc":"An electric log run inside a casing to confirm the top of cement behind the casing. In open hole it may used to determine the depth of water influx into the wellbore or the depth loss zone."},{"value":"Tensile strength","id":"647","desc":"The maximum longitudinal stress that a metal can bear without tearing apart. A metal?s tensile strength is greater than its yield strength."},{"value":"Thermally stable Poly-Crystalline Diamond Bit (TSP)","id":"648","desc":"The bit is also a fixed head bit like a PDC bit whose manufacturing process is similar to that of PDC bits (see polycrystalline diamond compact bit) but the TSP bits are more like natural diamonds in that they are more stable at relatively high temperatures than the PDC bits."},{"value":"Thixotropy","id":"649","desc":"A liquid (like the drilling mud) that contains suspended solids will keep the solids in motion in dynamic (circulating) condition. At static condition (when circulation stopped), the suspended solids will try to settle. Thixotropy is a character exhibited by the liquid that will hold the solids in suspension even when the circulation is stopped by gelling (called gel strength). The liquid becomes gelled at static state. This type of fluids exhibits non-Newtonian fluid behaviour."},{"value":"Thread compound","id":"650","desc":"See dope."},{"value":"Thribble","id":"651","desc":"It refers to a stand of pipe made up of three joints."},{"value":"Thribble board","id":"652","desc":"It is same as the monkey board or derrick man working platform that is used by the derrick man to handle the stands (thribble or doubles) while tripping. A thribble board is located at an appropriate height to handle and rack the thribble (a stand made of three joints)."},{"value":"Tight formation","id":"653","desc":"A formation with relatively low permeability."},{"value":"Tong Dice","id":"654","desc":"They are very hard and brittle pieces of serrated material designed to grip or bite the too joint of the drill pipe or collar when tongs are latched to apply the torque."},{"value":"Tongs","id":"655","desc":"See lead tongs, makeup tongs and breakout tongs."},{"value":"Tool joint","id":"656","desc":"Heavy special steel materials that are welded or screwed to a pipe at both ends. One end will be the pin or the male connection and the other end box or the female connections. The tool joins have the threads to make up connections with another pipe of similar threads. They are designed to sustain and withstand the weight of the drill string, the strain of very frequent coupling or uncoupling (making and breaking connections) while at the same time provide a leak proof connection seal so that mud or other fluids can be pumped at high pressure. A hard band made of tungsten carbide material is often applied around the outside of the tool joint to minimize or prevent wear due to abrasion from the walls of the well or the casing."},{"value":"Top drive","id":"657","desc":"It is a critical component of a rig?s hoisting, rotating and circulating system as it functions to satisfy all the three systems. A unique and versatile system that can be considered as an engineering marvel as it can simultaneously withstand loads up to 1 million pounds (the capacity can be even more), up to 5,000 psi pressure and rotate drill string even up to 200 or beyond rpm. In addition it can spin and torque a drill pipe connection. A modern top drive has replaced the swivel, Kelly, Kelly bushing, hook and rotary table with its own tongs to torque up."},{"value":"Torsional yield strength","id":"658","desc":"The amount of twisting or rotating force that a pipe can with stand before twisting off."},{"value":"Total porosity","id":"659","desc":"It is the percentage of the total pore space or pore volume in the total bulk volume of the rock."},{"value":"Trajectory","id":"660","desc":"The path of a wellbore. "},{"value":"Trap","id":"661","desc":"An impermeable body or rock that traps the migration of hydrocarbons and allow them to accumulate. "},{"value":"Traveling block","id":"662","desc":"It is one of the hoisting system components of a rig. The block is an arrangement of pulleys or sheaves through which drilling line is reeved. The traveling block has one sheave less than the crown block. The drill line is first reeved on the draw works drum (clamped at the fast end), then the line goes to the 1st sheave of the crown block and then to the 1st sheave of the traveling block and so on between the crown block and traveling block until all the sheaves are reeved. From the last sheave on the crown block the line is taken to the dead end line and clamped. The traveling block travels up and down in the derrick or mast to lift the pipe out of and lower the pipe into the hole by draw works power through the reeved drill lines."},{"value":"Trip or tripping","id":"663","desc":"A trip generally refers to pulling out the bit out of hole (either to change it or any other component of the BHA) and running in back to the bottom. Trip in is to run in hole and trip out is to pull out of the hole."},{"value":"Trip gas","id":"664","desc":"During drilling, mud is circulated. The annular pressure losses are transmitted as additional mud weight (see equivalent circulating density). However, when the circulation is stopped for a trip (see trip), the additional mud weight is temporarily lost until the circulation commences again. During this time or due to swabbing during tripping out, a relatively very small amount of gas may enter the wellbore. When the circulation commences again, this gas is circulated to surface and is recorded as trip gas. The trip gas is a critical component to identify the onset of high pressure zones or the degree of overbalance of the mud."},{"value":"Trip margin","id":"665","desc":"It is a safety margin in terms of a small additional mud weight over the value needed to balance the formation pressure. The extra pressure exerted by the additional mud weight although small is used to overcome any pressure reduction due to swabbing effect while tripping out of hole."},{"value":"Trip tank","id":"666","desc":"A small tank usually with a capacity of 30 barrels. It is marked with divisions of volume equivalent to displacement volume of pipe or with ? or 1 barrel divisions. It is used to show the level of mud in the trip tank and the amount of mud that is being filled in the hole while pulling out (it should be equal to the metal volume removed from the well) or the amount of mud returned from the well while running in hole (it should be equal to the metal volume of the pipe that is being run)."},{"value":"Trip tank indicator","id":"667","desc":"It shows the level of mud in the trip tank and the amount of mud that is being filled in the hole while pulling out (it should be equal to the metal volume removed from the well) or the amount of mud returned from the well while running in hole (it should be equal to the metal volume of the pipe that is being run)."},{"value":"Tubing","id":"668","desc":"Tubing is used as a completion string in a well to be a conduit for the flow of oil or gas from the reservoir to the surface. Tubing comes in different sizes, grades and thread connections to suit the requirements of the completion design."},{"value":"Tubular goods","id":"669","desc":"Any kind of pipe is referred as a ?Tubular?. In the oil industry, it is also called OCTG ? Oil Country Tubular Goods that includes drill pipes, casings, tubings, line pipe etc."},{"value":"Twist off","id":"670","desc":"The breaking of pipe in to two parts due to metal fatigue."},{"value":"Ultimate recovery","id":"671","desc":"Total ultimate estimated recovery of oil or gas from a reservoir rock."},{"value":"Unconformity","id":"672","desc":"It refers to a gap in the stratigraphic record due to lack of continuity in the deposition of rock strata between an older rock and a younger rock above it."},{"value":"Unconsolidated formation","id":"673","desc":"Loosely arranged sediments in a rock."},{"value":"Underbalanced drilling","id":"674","desc":"Normal drilling is done using a mud weight that exerts higher pressure than that of the formation. This is called overbalance. Underbalanced drilling is the opposite of it. The mud hydrostatic pressure is less than that of the formation. Due to this, the formation fluids will enter the wellbore. Drilling continues with a rotating head on the blow out preventer stack (see rotating head), which seals off the annulus and allow the formation fluids to be diverted away from the well. Underbalanced drilling has many applications but it requires extreme caution and management techniques."},{"value":"Underground blowout","id":"675","desc":"An uncontrolled flow of oil or gas or formation water from one reservoir into the wellbore, along the wellbore and into another reservoir. It normally occurs during a kick situation. When the kick is recognized, the blow out preventer is shut in. As the formation pressure is higher than the mud hydrostatic pressure, the surface pressure keeps increasing. If this pressure is high enough to fracture a week zone at a different depth, the formation fluids from the kick zone will start flowing to the fractured zone uncontrollably."},{"value":"Under ream","id":"676","desc":"Once a casing is run and cemented, the next whole size will be a maximum of the casing drift diameter. If a hole size is required bigger than this to meet the well design, then under reamers are used. The hole will be drilled first with the maximum size bit possible to run inside the casing (pilot hole) and then it is underreamed to enlarge the hole to the required size. It is also referred to enlarge a pilot hole without the restrictions of a casing inside diameter but in that case mostly a hole opener is used."},{"value":"Updip","id":"677","desc":"In a dipping plane or surface, updip indicates a position upside of a specified point. Downdip is to the downside of the specified point. In a reservoir rock, the lighter fluid gas is accumulated in the updip side and water the heavier fluid is at the downdip side with oil in-between."},{"value":"V-door","id":"678","desc":"V-door is an inclined surface connecting the rig floor and the cat walk normally opposite to the draw works and the driller (to have a good visibility). The pipes are first placed on the catwalk, which is then pulled by air hoists that drags along the V-door. The pipe rests with its box end at the top of the V-door and the pin end at the bottom of the V-door. When required, the pipe is picked up from the V-door. Drill pipes, casings or tubings are generally picked from catwalk through the V-door."},{"value":"Vertical seismic profile (VSP)","id":"679","desc":"It is a type of borehole seismic measurement that is used for correlation with the seismic data. It uses geophones in the well bore with the source at the surface near the well. It is run on a wireline logging unit. There are many types of VSP ? check shot (it is not exactly a VSP but serves to check the velocity-depth profile locally and is not as detailed as a VSP), walk away VSP (for directional wells), zero offset VSP, offset VSP etc."},{"value":"Viscosity","id":"680","desc":"It is a measure of the resistance of a fluid flow. In drilling, viscosity of drilling mud is a critical parameter. Its unit is poise or centipoise. For field measurements of viscosity, see funnel viscosity."},{"value":"Virgin pressure","id":"681","desc":"It is referred the original undisturbed pressure of the formation."},{"value":"Water base mud","id":"682","desc":"Drilling mud in which water is the continuous phase. Many chemicals and additives are added to provide the required properties of the drilling mud."},{"value":"Wall cake","id":"683","desc":"See filter cake."},{"value":"Water drive","id":"684","desc":"A type of drive mechanism that helps to force the oil to flow to the wellbore. In general, there are two types of water drive. One is bottom-water drive in which the water is beneath the oil and the other is edgewater drive in which only a portion of the oil is in contact with the water."},{"value":"Water loss","id":"685","desc":"See fluid loss."},{"value":"Water saturation","id":"686","desc":"The percentage of water in the reservoir fluid filled in the pores of the reservoir. See saturation."},{"value":"Washout","id":"687","desc":"An enlargement of wellbore from its gauge size caused by erosion or swelling and sloughing of shales or falling of loose unconsolidated formation etc. A caliper log indicates the gauge of the hole."},{"value":"Weight on bit (WOB)","id":"688","desc":"The weight or downward force applied on the bit by the weight of drill collars in order to drill."},{"value":"Weighting material","id":"689","desc":"A chemical like barite or galena that has high specific gravity and is used to increase the density of drilling muds."},{"value":"Wellbore","id":"690","desc":"It is the hole drilled in a well."},{"value":"Wellhead","id":"691","desc":"It is an equipment installed at the surface of the well where casings are terminated by hanging the casings using casing hangers and seals. The wellhead provides the pressure seal as well as the strength to hold the hanging weight of casings. It is also used to hang a completion tubing and to install a production X-mas tree on top of it."},{"value":"Well completion","id":"692","desc":"See completion."},{"value":"Well control","id":"693","desc":"It refers to controlling the well in a kick situation. Once a kick is encountered, the influx (kick fluids) must be circulated out safely without allowing any further influx and at the same time displace the well with the correct kill mud such that the well comes under control. This term also refers to taking all the precaution to prevent a kick and keeping the well under control at all times. This requires adequate mud weight in the hole such that it is always higher than the formation pressure, keeping the hole full at all times, prevent swabbing during pulling out of hole, well trained crew etc."},{"value":"Well logging","id":"694","desc":"Log generally means records. A well log means recording of information while drilling a well. This includes records of driller?s reports, mud logging, mud reports, core analysis, drill stem test, wireline logging etc."},{"value":"Wildcat","id":"695","desc":"It is a pure exploration well in an area where no offset wells exist or subsurface information from actual drilling is not available. The well is drilled only with the seismic data interpretation with no correlation with nearby wells."},{"value":"Wiper trips","id":"696","desc":"Wiper trips that are made in between the drilling process (before reaching the section depth) generally to prove the hole already drilled to clean the hole, wipe swelling clays or clear tight spots or to prove the hole prior to running casing or in between wireline logging operations. Excess wiper trips may be detrimental to the well and hence wiper trips must be planned only as necessary."},{"value":"Wireline logging","id":"697","desc":"An electric log that is run on wireline to record certain parameters and physical properties of formation and formation fluids. The main purpose of the wireline logs is to identify the formation fluid, the thickness, contact between oil and water (or oil and gas or oil and water etc), formation pressures, formation fluid samples under reservoir conditions, cores etc."},{"value":"Work over","id":"698","desc":"The term refers to work over a well and the work means several ways to intervene a producing well to conduct remedial operations to improve production from the well. It includes but not limited to additional perforations, new zone perforations, isolating certain zones, change completion string (like adding a gas lift mandrel) etc."},{"value":"Work over rig","id":"699","desc":"A portable rig that is used conducting work over operations in a well."},{"value":"X-Mas tree","id":"700","desc":"It is an assembly of valves and gauges that is installed above the wellhead of a completed well. It is used to control the production. It also allows well intervention to run wireline tools subject to a lubricator installed above it. It normally has one or two master valve(s), wing valve, a swab valve and a tree cap. To the wing valve, a choke is connected that is used to control the flow and production."},{"value":"X-C polymer","id":"701","desc":"It is a polysaccharide polymer known as xanthan gum. It is used in water based mud system to control the rheology especially to increase the viscosity and yield point. It also helps moderately to control fluid loss."},{"value":"X-Ray diffraction (XRD)","id":"702","desc":"It is a technique used for mineralogical analysis of a rock by measuring the diffraction peaks of the rock but it is semi quantitative only. It is especially used in drilling for clay analysis to determine the best mud systems to be used if the clay is reactive."},{"value":"Yield","id":"703","desc":"In drilling mud, it represents the number of barrels of a specified viscosity a ton of clay will produce. In cementing, it represents the volume occupied by one sack of cement after mixing with water for a specified slurry weight. In drilling, it represents a minimum yield strength of a pipe. For example, a N-80 casing has a yield of 80,000 psi."},{"value":"Yield point","id":"704","desc":"It is a parameter of mud rheology and is used to evaluate the ability of mud to lift the cuttings efficiently out of the annulus. An optimum yield point is essential for effective hole cleaning. It is also expressed as the maximum stress that a steel (or any solid) can withstand without under going permanent deformation."},{"value":"Zero offset VSP","id":"705","desc":"It is a conventional VSP in which the source is positioned directly above the receivers very close to the wellbore."},{"value":"Zone of lost circulation","id":"706","desc":"A zone or formation where loss circulation occurs."}]