Oil and Gas Industry Terminology


If you're new to the oil and gas world, or are even just considering an energy-relate...

NES Fircroft

By NES Fircroft

If you're new to the oil and gas world, or are even just considering an energy-related job at this stage, our "Oil & Gas Terminology Series" will help you get clued up with some of the industry's jargon. 

We've compiled our previous series into a single, comprehensive blog with the key terms and acronyms used by the industry. You can use the menu below to navigate this list. 

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Associated Gas

Natural gas produced with crude oil from the same reservoir, or that which is associated with oil accumulations, which may be dissolved in the oil at reservoir conditions or may form a cap of “free gas” (in a gaseous, not liquid state) above the oil.

Appraisal Well

A well drilled as part of an appraisal drilling programme which is carried out to ascertain the size, reserve and estimated production rate of an oil field.


A chemical additive used to lower interfacial tension so that trapped gas will readily escape from mud and not form a foam. This additive is used during the preparation of a treatment fluid or when preparing the drilling surface (slurry). Common additives include: Octyl alcohol, aluminum stearate, various glycols, silicones and sulfonated hydrocarbons.

Treatment fluid - A fluid designed and prepared to resolve a specific wellbore or reservoir condition. Treatment fluids are generally prepared at the wellsite for purposes such as stimulation, isolation or the control of reservoir gas or water. Every treatment fluid is designed for specific conditions.

Slurry - A term used to describe a mixture of suspended solids and liquids. 

Alkaline Flooding

Also known as “caustic flooding”, this is an oil recovery technique in which an alkaline chemical such as sodium hydroxide is injected during polymer flooding or waterflooding operations. The alkaline chemical reacts with the oil, forming surfactants inside the reservoir, which reduce the interfacial tension between oil and water and therefore enable an increase in oil production.

During “waterflooding”, water is injected into the reservoir to displace residual oil. The water moves the displaced oil to adjacent production wells.

“Surfactants” are compounds that lower the surface tension between two liquids, or two items of opposing states, i.e. between a gas and a liquid, or between a liquid and a solid. 

Abrasive Jetting

A wellbore treatment in which a fluid containing solid particles is used to remove deposits from the surface of the wellbore and / or completion components. The fluid is pumped at high pressure through a downhole tool that uses nozzles to direct jets of the fluid onto the target area. Many tools utilise a controlled rotary motion to ensure the entire internal circumference of the wellbore is treated. Abrasive jetting can also be used to cut completion or wellbore components in which case highly abrasive particles (such as sand) are put into the fluid and then jetted at the target area for a prolonged period of time until the surface is eroded.

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Barrel or Barrel of Oil EQ (BOE)

A unit of energy used to measure the volume of petroleum and related products. It’s based on the approximate energy released by burning one barrel or crude oil.


Refers to a barrel of oil. One barrel of oil is approximately 35 imperial gallons or 159 litres. Oil companies typically use BBL to report on their production. You many sometimes see it listed as Mbbl which refers to one thousand barrels or MMbbl which refers to one millions barrels.


Refers to a billion cubic feet of natural gas. It’s used to measure the amount of natural gas that is untapped or currently being pumped.


Means a ‘billion cubic metres’ and is generally used to measure natural gas. One billion cubic metres (BCM) is equivalent to 35.31 cubic feet.


A drilling tool used to cut a cylindrical hole in the earth’s crust – sometimes referred to as a ‘drill bit’ or ‘rock bit’. It can be used during the discovery or extraction process of both crude oil and natural gas. The diameter of the hole it creates can vary from 3.5inches up to 30 inches and it can create hole depths of up to 30,000 feet.


A geographical area of land in which an oil or gas reservoir lies. A ‘Block’ will be awarded to drilling and exploration companies and the land mass is usually measured in 1000s of sq. kilometers.


When well pressure exceeds the ability of the wellhead valves or drilling mud, which causes oil and gas to 'blow' to the surface – in other words it’s an uncontrolled release of either crude oil and/or natural gas. In some cases, blow-outs can be extremely dangerous – an accidental spark can lead to a fire breaking out.

Blow-Out Preventer

A specialised mechanical device or valve which prevents blow-outs. It’s used to both seal and monitor the well in order to control pressures associated with drilling oil and gas.


The hole made by the drill, which includes the open hole or uncased portion of the well. It can refer to the inside diameter of the wellborn wall or in other words, the rock face that bounds the drilled hole.


Means ‘British thermal unit’ which is a measurement unit of the heating value of a fuel.

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A company’s capital expenditure in the current year. Its money the organisation uses to improve its fixed assets such as land, equipment, vehicles or buildings.


When ions in groundwater chemically precipitate and form a new crystalline material between sedimentary grains.


Rocks that are composed of fragments or broken pieces of older rock.

Commercial field

When an oil and/or gas field is judged to be worth developing. It means the field is capable of producing enough net income, at low risk, to make it economic for development. The opposite of this is a Marginal Field – this means the oil field may not produce enough net income to be worth development.


The process of making a well ready for production after drilling operations. It usually involves the installation of permanent wellhead and downhole equipment.


A mechanical device, such as an engine, used to reduce the volume of gas so it can increase the pressure. This allows the gas to flow more easily through a pipeline or from a reservoir.

Contingent resources

Quantities of petroleum estimated, as of a given date, to be potentially recoverable from known accumulations. However, the project(s) are not yet considered mature enough for commercial development.

Conventional Oil

Oil found or expected to be found within a conventional reservoir. Usually, it refers to crude oil, petroleum or raw natural gas.

Core and Coring:

A term associated with drilling. Coring is the process in which a continuous cylindrical sample of rock from the wellbore is taken to assess the productivity of oil well drilling. Normally it’s taken in 30 ft sections using a “core barrel” tool. This process provides valuable information about the rock being drilled and can be used during the exploration phase.

Creaming Curve

A statistical technique used to present the relationship between aggregated or cumulative resource from wells drilled.

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A tower-like structure where drilling controls and lifting equipment are typically housed

Development Well

A well drilled in a proven area of an oil or gas reservoir with the goal of maximising economic production and recovery of reservoirs known reserves. They are typically drilled to the depth of a stratigraphic horizon that is known to be productive. The probability of success increases as more development wells are drilled. Development wells differ to exploratory wells as they are wider in diameter and drill deeper.


When a petroleum accumulation is found following several exploratory wells. Testing, sampling and/or logging the existence of a significant quantity of potentially moveable hydrocarbons must take place before a discovery can be declared.


Tools, instruments and equipment used in the wellbore or techniques applying to the wellbore.


This term indicates the refining of petroleum crude oil or the processing of natural gas as well as the marketing and distribution sectors of the oil and gas industry.

Drill mud

Drilling fluid that is used to clean and lubricate equipment during the drilling process as well as recover samples of the sub-surface formations to surface whilst counteracting the natural pressure of a formation. 

Drilling rig

A drilling component that isn’t permanently fixed to the seabed. For example, a drillship or a jack-up unit. The term ‘drilling rig’ also can refer to the derrick and its associated machinery. Although this term is usually used in offshore activities, you may also hear it during discussions of onshore for land-based drilling activities.

Dry gas

Natural gas composed mostly of methane. It can have minor amounts of ethane, butane and propane and, generally, has little or no heavier hydrocarbons.

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Abbreviation for “exploration and appraisal”


Abbreviation for exploration and production

  • Exploration - refers to the search for oil and gas; methods can include aerial surveys, geophysical surveys, geological studies, core testing and the drilling of test (wildcat) wells.
  • Appraisal - The phase of the petroleum project that immediately follows successful exploratory drilling. During appraisal, delineation wells are often drilled to ascertain the size of the oil or gas field and the most efficient method for development.
  • Production - The phase that occurs after successful exploration and development – during this time the hydrocarbons start to be drained from the oil or gas field.


Applies to drilling equipment whereby steel components become less resistant to breakage and significantly weaker in tensile strength as a result of prolonged exposure to gaseous or liquid hydrogen sulphide. The weakness is caused when hydrogen ions get between the grain boundaries of the steel, where they then form molecular hydrogen – this takes up more space and reduces the strength of the bonds between the grains. Molecular hydrogen can cause metal to crack when subjected to tensile stress. Hydrogen embrittlement can also be referred to as “acid brittleness”.

Enhanced oil recovery (EOR)

A process which uses sophisticated techniques to increase the amount of oil that can be recovered from an oil reservoir. It restores formation pressure, and improves oil displacement / fluid flow in the reservoir. There are 3 major recovery types: chemical flooding (alkaline flooding or micellar polymer flooding), miscible displacement (carbon dioxide injection or hydrocarbon injection), and thermal recovery (steamflood or in-situ combustion). Enhanced oil recovery is also known as “improved oil recovery” or “tertiary recovery” and it is generally abbreviated to EOR.

Exploration Well

A concentrated area where drilling is carried out to determine whether hydrocarbons are present in a particular area or structure. Sometimes known as a ‘wildcat well’, particularly in places where little drilling has taken place previously.

Erosion corrosion

A type of corrosion produced when scales such as iron carbonate that initially protected the metal surface of the pipe have become eroded, meaning that the underlying metals begin to corrode - this is a common cause of failure in oilfield equipment and in particular, intersecting pipe sections, bends or elbows where there is high velocity or turbulent flow are most at risk.

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An area under which a large amount of oil or gas lies. The size of an oilfield can vary hugely in size – some of the world’s largest, such as the Rumailia field in Iraq, produce millions of barrels of oil every day.


Not necessarily a creature with scales! In the oil and gas world, anything left in a wellbore, be it junk metal (generally remnants of milling operations), hand tools, a length of drillpipe – anything lost down there is simply referred to as “the fish”. Anything put into the hole should be accurately measured so that appropriate tools can be used to retrieve the object.


Refers to the act of retrieving objects from the borehole. For retrieval to be successful, the operation requires an understanding of the dimensions and nature of the “fish” to be recovered, the wellbore conditions, the tools and techniques to be employed and the process by which the recovered fish will be handled at surface.


A method of breaking down a rock formation by injecting fluid at very high pressure so as to force open existing fissures, with the ultimate aim of increasing the reservoir’s production rate through making it easier to extract fuel from the field.

Fracturing Fluid

Fracturing fluids for shale reservoirs usually contain water, proppant, and low levels of nonaqueous fluids designed to reduce friction pressure whilst pumping the fluid into the wellbore.

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Gas Field

A field that contains natural gas only. Sometimes there may be limited producible oil but this is rare. 

Gas Injection

A process used to maintain reservoir pressure. Separated associated gas will be pumped back into a reservoir for conservation purposes.

Gas in Place (GIP) or Gas Initially in Place (GIIP)

Before extraction or production takes place, GIP or GIIP refers to the quantity of estimated gas that is believed to exist in naturally occurring accumulations.

Gas Lift

The process of raising or lifting fluid from a well by injecting gas through tubing into the well. The injection of gas means the fluid is aerated and less dense, forcing it out of the well bore.

Gas Oil Ratio (GOR)

Refers to the number of cubic feet of gas produced per barrel of oil


Any person or vehicle (i.e truck or barge) authorised to gather or accept oil, gas or geothermal resources after production or from storage.

Gathering Line

(or a pipeline) is located within an oilfield and gathers produced oil and/or gas with the purpose to bring it to a location for further transmission.

Gun Barrel Separator

Used to separate oil, water and gas and is located near the wellhead. 

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Horizontal Drilling

A method of drilling where the drill bit is turned in a horizontal direction (generally with an inclination greater than 85°) in an effort to produce hydrocarbons from a number of areas located at the same approximate depth.

Hot Oiling

Circulation of heated fluid (typically oil) to dissolve / dislodge paraffin deposits from the production tubing. Paraffin deposits can occur where a large variation in temperature exists across the producing system.

Hydraulic Disconnect

A downhole tool designed to allow the lower and upper tool string sections to be parted, which enables the retrieval of the running string. Hydraulic disconnects rely on the application of a predefined pressure through the running string to activate a release mechanism. Sometimes, a ball will be used to block circulation through the tool string, which enables the application of the release pressure.

Running string - A small-diameter tubing string run inside the production tubing of a well as a remedial treatment to resolve liquid-loading problems. As the reservoir pressure in a gas well depletes, there may be insufficient velocity to transport all liquids from the wellbore.


A compound that contains only the elements hydrogen and carbon; this can exist as a solid, a liquid or a gas.

Hydrochloric Acid

A type of acid commonly used in oil and gas well stimulation, especially in carbonate formations (rock where the main mineral content is calcite and aragonite). The effects of hydrochloric acid enable it to be used in many treatments, often with chemical
additives that enhance its performance or allow greater control of the treatment. Treatments are commonly conducted with 15% or 28% solutions of hydrochloric acid.

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Industry Mutual Hold Harmless (IMMH)

An indemnity scheme run by LOGIC in the UK. The scheme was set up with the primary objective of addressing the contractual gap which traditionally exists between contractors and sub-contractors. The IMMH is designed to sit as a background agreement where there has been no direct contract between contractors.

Improved oil recovery (IOR)

Processes that improve the flow of hydrocarbons from a reservoir to the wellbore. It sometimes refers to the recovery of more oil or natural gas than expected. Enhanced oil recovery (EOR) is an example of IOR.

Infill Wells

Wells drilled into an existing reservoir between wells that are already producing oil/natural gas so the product does not have to travel as far through the formation. The increase in the number of wells per unit area improves recovery efficiency.

Injection Well

A well in which water or gases are injected into the reservoir. Typically this is done to maintain reservoir pressure.

In-situ recovery

Techniques used to extract hydrocarbons from beneath the surface without removing the soil and other materials.

Internet of Things (IoT)

A system of interrelated physical devices, appliances, machines and more that enable connectivity and shared data without human interaction. Like many other industries, the Oil and Gas sector is increasingly adopting the Internet of Things to improve their data.

Integrated company

A term used to indicate that a firm operates in both the upstream and downstream sectors.

Industry Technology Facilitator (ITF)

An Oil and Gas trade organisation established in 1999. The purpose
of the ITF is to support the development of new technologies and innovation within the sector. It’s internationally recognised and has many of the world’s largest Oil and Gas companies as members.

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The lower section of an offshore platform. Sometimes, this section can also be called the ‘legs’.

Jacking Frame

A hydraulically controlled support structure used to stabilize the injector head and pressure-control equipment on coiled tubing units. They are most commonly found on offshore units but can also be found on some special onshore units.

Jackup Rig

An offshore drilling system commonly used in water depths of 50-330ft. They are made up of a drilling rig, floating barge, and are fitted with long support legs that can be raised or lowered
independently of each other. If the ocean bottom is firm, an independent leg will be used whereas if the ocean bottom is soft, the rig will be mat supported.

Jamin Effect

An increase in flow resistance, commonly when one (or more) interfaces are present at one time in a channel.


A tool used in drilling or workover and is either hydraulic or mechanical. The tools purpose is to deliver a sharp upward or downward blow to the tools below it. An example of its use is to free a tool or bit that is stuck. A jar accelerator, booster or intensifier can be used to speed up or increase the effect of the jar.


A high-velocity drilling fluid stream from a nozzle or bit. It’s used to drill a seismic shot hole.

Jet Hopper 

A mud-flow device, (sometimes called a mud hopper) that is used to feed materials into a jet mixer which is a mechanical blender used to mix a dry material* with drilling mud. The jet hopper is powered by a centrifugal pump that allows the materials to flow at a high velocity.

*Dry materials are added to provide dispersion, rapid hydration and uniform mixing.

J factor 

(sometimes called the pseudo-geometrical factor) is a term used during the well-logging process. Well logging measures the depth and subsurface formation during drilling – the J factor is the response of a logging measurement as a function of distance from the tool.


A length of pipe, and usually refers to tubing, drillpipe or casing.


The cooling of gas as it expands. This effect is sometimes called the ‘throttling effect’ and can be used to cool produced gas therefore removing natural gas liquids and hydrates.

Junk pusher 

A downhole tool that prepares the casing for setting a packer. It works similarly to a casing scraper and ensures the wellbore is unobstructed before setting a packer or similar fullbore device. It is used with a gauge ring.

Junked and abandoned (J&A) 

A well that has been abandoned due to a drilling problem.

J Slot 

A type of mechanism commonly used to set and unset downhole tools*, like packers. It’s named this way because the slot is shaped like a J. The short side supports the protrusion weight and the long side is open to release the protrusion. A J Tool fits into the J Slot.

*Most conventional downhole tools operate upward, downward or they rotate.

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A clay mineral that forms through the weathering of feldspar and mica group minerals. Unlike some clay minerals, kaolinite is not prone to shrinking or swelling with changes in water content.


A type of topography formed in areas of widespread carbonate rocks through decomposition. Typical features of karst topography include sink holes, caves and pock-marked surfaces.


A long square or hexagonal steel bar hollowed out in the middle to make way for a fluid path. The Kelly is used to transmit rotary motion from the Rotary Table or the Kelly Bushing to the Drillstring, whilst allowing the Drillstring to be lowered or raised during rotation. The Kelly goes through the Kelly Bushing, which is driven by the Rotary Table, and turns the entire Drillstring because it’s screwed into the top of the Drillstring itself.

Kelly Bushing

Sometimes known as “Drive Bushing”, this is a tool that serves to connect the Rotary Table to the Kelly. The Kelly Bushing tool’s inside profile matches the Kelly’s outside profile, so that the Kelly can move up and down inside the tool. The rotary motion from the Rotary Table is transmitted to the Bushing through large steel pins, and then to the Kelly itself through the flat surfaces between the Kelly and the Kelly Bushing.


Depth measurements are commonly referenced by “KB”, such as 5,000 ft KB, meaning 5000 feet below the Kelly Bushing.

Drillstring: the combination of the drillpipe, the bottomhole assembly and any other tools used to make the drill bit turn at the bottom of the wellbore.

Rotary table: A drill floor with spinning sections that are used to transmit power and rotary motion through the Kelly Bushing to the Drillstring.


A small-diameter channel worn into the side of a larger diameter wellbore. Often this results from a sharp change in direction of the wellbore, or if a hard formation ledge is left between softer formations that then enlarge over time. The diameter of the channel is generally similar to the diameter of the drill pipe, which causes problems for the larger diameters of drilling tools such as tool joints, drill collars and bits, as they unable to pass through the channel and may become stuck in the key-seat. Preventive measures include ensuring that any turns in the wellbore are gradual and smooth. The solution to key-seating is to enlarge the worn channel so that the larger tools will fit through it.

Kill Line

A high-pressure pipe connecting the mud pump and the well, through which drilling fluid can be pumped into the well to control a threatened blowout. During well control operations, kill fluid is pumped through the drillstring and annular fluid is taken out of the well through the choke line, which controls the fluid pressure. If the drillpipe is inaccessible, it may be necessary to pump heavy drilling fluid into the top of the well, wait for gravity to force the fluid to fall, and then remove fluid from the annulus, via both the kill line and choke line. The kill line also provides a measure of redundancy for the operation. In floating offshore operations, the choke and kill lines exit the subsea BOP stack and run along the outside of the riser to the surface.

BOP stack: is one of two or more units which control well pressure, and contain the wellhead and blowout preventers.

Choke: used to control fluid flow rate or downstream system pressure. Chokes have varying configurations -adjustable chokes enable the fluid flow and pressure parameters to be changed to suit process or production requirements.

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Lag Time

The time taken for cuttings to reach the surface. The term is also used in place of cycle time.


A legal document conveying the right to drill for oil and gas i.e. begin exploration of production activity within a specified area.

Liquefied natural gas (LNG)

Naturally occurring gas (primarily methane and ethane), which is liquefied for transportation. Natural gas becomes a liquid at the very low temperature of minus 258 degrees ºF and may be stored and transported in the liquid state. This process is often required when a gas pipeline is not available to transport gas to the market place – such as remote jungle areas and offshore.

Liquefied petroleum gas (LPG)

Gas mainly composed of propane and butane (light hydrocarbon material), which is gaseous at atmospheric temperature and pressure, held in the liquid state by pressure to facilitate storage, transport and handling. The gas is obtainable from refinery gases or after the cracking process of crude oil. Commercial liquefied gas consists essentially of either propane or butane, or mixtures thereof, and is also referred to as “bottled gas”. The ease of conversion to a gaseous state means it can be used industrially or domestically.

Liquid Desiccant

A hygroscopic liquid used to remove water / water vapour from a gas stream. Some are glycols (diethylene, triethylene and tetraethylene), which are substances that can be regenerated i.e. the water
absorbed by these substances can also be separated from them. Some liquid desiccants however, such as methanol or ethylene, cannot be regenerated.

Live Oil

Oil containing dissolved gas in solution (gas that is dissolved in a liquid, such as water or oil) that may be released from solution at surface conditions. Live oil must be handled and pumped under closely controlled conditions to avoid the risk of explosion or fire.

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A unit of measurement for ‘thousands of barrels’.


A unit of measurement stands for ‘measured depth’.

Medium Crude Oil

Liquid petroleum that has a density between light and heavy crude oil.

Metric tonne

A unit of measurement equivalent to 1000 kilos, 2204.61 lbs; 7.5 barrels.


The main constituent of natural gas. Chemically, it’s classed as the simplest hydrocarbon molecule and is made up of on carbon atom and four hydrogen atoms.


An acronym for ‘maximising economic recovery’. It is a process of ensuring economic viablity and return of oil and gas drilling projects, offset by their cost.

Middle Distillates

Medium-density refined petroleum products such as jet fuel, kerosene and light fuel oil.

Miscible Flooding

Refers to an oil recovery process. Fluid that is able to mix completely with oil is injected into the oil reservoir with the aim of increasing recovery.


A unit of measurement for 'millions of barrels'


A unit of measurement for ‘million barrels of oil equivalent’.


Acronym for ‘millions of cubic feet per day’ (of gas). This unit of measurement is predominantly used in the United States.


Also known as ‘drilling mud’ or ‘drilling fluid’, mud is a heavy fluid mixture made of base substance and additives that is used to lubricate and cool the drill bit.


The oil and gas industry is divided into three major components: upstream, midstream and downstream. Midstream is a term used to refer to activities, such as transportation, that fall between exploration and production (upstream) and refining and marketing (downstream).

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Natural Completion

Refers to a completion system that utilizes the natural flow capability of a reservoir.

Natural Gas

Gas that occurs naturally. It is often found with crude petroleum.

Natural gas liquids ( or NGLs)

The portions of gas from a reservoir that are liquefied. This is usually observed in gas processing plants, at the surface in separators or field facilities. Sometimes NGL is also called liquefied petroleum gas (LPG).


A chemical reaction between a base and an acid which forms salt and water. This process is used in the manufacturing of mud products or the removal of acidic products/contaminants from muds. It is also used to test how alkaline a mud is.

Neutron Log 

A radioactivity well log that determines how porous a formation is by blitzing the formation with neutrons. As the neutrons hit the hydrogen atoms in oil or water, gamma rays are released which are then used to identify the porosity.

Night Toolpusher

The job role ‘Assistant Toolpusher’ who generally works during night-time hours.


A type of pipe fitting that is tubular in nature and threaded on both ends. It is used to connect pipe joints and other tools.

Nitro Shooting

A formation-stimulation process where Nitroglycerine is placed in a well and exploded causing a fracture.


Acronym for Northern North Sea.

Non-Associated Gas

Natural gas from a reservoir that does not contain a significant amount of crude oil.


The passage through jet bits that cause drilling fluid to be ejected at a high velocity.

Nuclear tracer 

Gas, liquid, or solid material that emits gamma rays.

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Oil field

An accumulation, pool or group of subsurface oil pools. An oil field consists of a reservoir that traps hydrocarbons from being covered by impermeable or sealing rock. It may also contain associated gas.

Oil in place

An estimated measure of the total amount of oil contained in a reservoir, and, as such, a higher figure than the estimated recoverable reserves of oil.


The company that has legal authority to drill wells and undertake production of hydrocarbons. The operator is often part of a consortium (an association of several companies) and acts on behalf of this consortium.


An abbreviation for “operating expenditure” - an expense a business incurs through its normal business operations. Operating expenses can include rent, equipment, inventory costs, payroll, insurance and funds allocated for research and development.

Overboard Water

Another name for produced water or brine produced from oil and gas wells - water produced from a wellbore that is not a treatment fluid. The characteristics vary and use of the term often implies an unknown composition. It is generally accepted that water within the pores of shale reservoirs is not produced due to its low relative permeability and that fact that its mobility is lower than that of gas.

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Typically refers to liquid crude oil - a complex mixture of naturally occurring hydrocarbon compounds which are found in rock. The colour, odour, sulphur content, gravity and viscosity varies considerably in petroleum found in different areas.


The capability of a rock to allow passage of fluids through it, usually measured in “millidarcies” or “darcies”.


An offshore structure that is permanently fixed to the seabed. In the context of Oil, this structure is part of the system used to extract oil from the ground.

Proven field

An oil and/or gas field whose physical extent and estimated reserves have been effectively determined.

Proven reserves

Reserves which on the available evidence are judged to be technically and economically producible (i.e. having a better than 90% chance of being produced).

Primary recovery

Recovery of oil or gas from a reservoir purely by using the natural pressure in the reservoir to force the oil or gas out of the wells and up to the surface.

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Planned monitoring, testing and documenting of practices to show that a product or procedure meets established standards. Companies that deal in drilling fluid materials i.e. those that manufacture, process, sell, handle, ship or buy them, typically establish QA programmes, with some oil company labs also performing QA testing. API (American Petroleum Institute) and ISO (International Organization for Standardization) jointly issue specifications for mud materials. Generally, a mud supplier must meet certain specifications and adhere to quality testing practices in order to place an API logo on their product – suppliers are also required to pay to be eligible to use the logo.


A unit of measurement – a quadrillion of BTU's- used in connection with energy consumption. A barrel of crude oil contains 5.8 million BTU's, whereas natural gas contains about one million BTU's per MCF.

Quench Oil

Oil that is used to harden steel by controlling the heat transfer during the quenching process, enabling consistent metallurgical properties. Apart from hardenability, the oil can tolerate some other factors like thickness, degree of distortion and geometry.


A chemical with the formula CaO, sometimes called hot lime. When hydrated with one mole of water, it forms slaked lime, Ca(OH)2. Quick lime is generally used in preference to slaked lime at oil mud mixing plants because it generates heat when it becomes slaked with water, speeding up emulsification to form calcium fatty-acid soap.

Quitclaim Deed

A legal document pertaining to the transfer of any mineral rights, royalty interests and overriding royalty interest owned by any royalty interest owner, to oil and gas mineral acquisition organisations or any drilling organisation with no warranty of title. The entity who owns the mineral rights is called the “grantor” - when the grantor transfers royalty interests to another entity, this entity is called the “grantee”. This document does not contain any title covenant and therefore offers no warranty of title to the grantee.

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The act of confirming the existence and terms of an oil and gas lease.


The completion of production of an existing well bore that has been previously completed (usually in another formation).

Recoverable resources

Quantities of resources estimated to be recoverable from known accumulations.

Recovery Factor

The ratio of recoverable oil and/or gas reserves compared to the amount of estimated oil and/or gas in the reservoir.

Regulatory Agency

A public authority that administers oil and gas policies set by the government. These bodies also serve as the source for public data related to any oil and gas operations within their area.


The quantities of oil and/or gas anticipated to be commercially recoverable from a reservoir. 

Reserve Pit

A pit used during drilling operations to both collect spent drilling fluids and wash water.


A permeable and porous sedimentary rock that contains oil and gas.

Residue Gas

Gas left over after the processing and extraction of natural gas liquids.

Riser (drilling)

A pipe between a seabed blowout preventer and a floating drilling rig.

Riser (production)

A section of pipework that joins the Christmas tree to a seabed wellhead. 


Drill crew members working on the derrick floor, screwing together the sections of drillpipe.


Drill crew members who manage the loading and unloading of equipment on a rig. They may also assist in general operations.


A percentage of interest paid to the mineral rights owner during production. 

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Secondary recovery

(a stage of Enhanced Oil Recovery) the recovery of oil and/or gas from a reservoir by injecting gas, water or other substances into the reservoir rock to sweep oil and/or gas from the reservoir. 


The use of elastic energy waves (such as P-waves and S-waves) to ascertain the nature of subsurface geological structures. 2D Seismic records are studied by scientists to interpret the composition, fluid content, extent, and geometry of rocks in the subsurface. 


 When liquid, gas hydrocarbons and water are separated. This is typically accomplished in a pressure vessel at the surface, but new technologies have been developed that allow separation to occur in the wellbore (under certain conditions). 


When production is paused to allow essential maintenance work to take place. 


Southern North Sea.


When the first part of a new well is drilled. 

Standard Contracts

(Known formerly as CRINE contracts) are the contracts developed by the ‘Standard Contracts Committee.’ They are issued for use between clients and their contractors to simplify procedures and save costs.

Standard Agreements

Agreements recommended for use by all UKCS licensees. They help to simplify operational and transactional procedures and focus on saving costs. 

Step Change in Safety 

A UK based partnership founded in 1997 by the oil and gas industry trade associations to reduce the UK offshore oil and gas industry injury rate by 50%.


A popular geospatial vector data format for geographic information system (GIS) software.

Suspended Well

A well that has been capped off temporarily.

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Top Side

The superstructure of a platform.

Tight Gas

Natural gas produced from reservoir rocks with such low permeability that massive hydraulic fracturing, where fluid is pumped into the ground to make it more permeable, is necessary to produce the well at economic rates.


The smallest diameter pipe within a well bore which transmits the hydrocarbon production to the surface.


Second-in-command of a drilling crew. Responsible for the day-to-day running of the rig and for ensuring that all the necessary equipment is available. Also called a rig superintendent, drilling foreman, or rig supervisor.

Thermal Recovery

A type of improved recovery in which heat is introduced into a reservoir to lower the viscosity of heavy oils and to facilitate their flow into producing wells.

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An abbreviation for ‘ultra large crude carrier.’


A term that refers to any particle with a size range between 2 to 44 microns.

Ultra-Heavy Oil

A term used to describe a hydrocarbon fluid with a gravity of 10° API or lower.

Ultrasonic Caliper

A device that uses high-frequency acoustic signals to measure the internal diameter of an open borehole, tubing or casing. A transducer emits the high-frequency signal which is then reflected back by the item being measured. The diameter is determined by the time it takes for the signal to return (echo) and the fluid acoustic velocity.


The Oil and Gas industry is divided into three sectors, Upstream, Midstream and Downstream. Upstream refers to the early stages of exploration and production, including drilling and extraction.


Stands for ‘United Kingdom Continental Shelf’ which is the offshore waters of the UK Sector.

Undersaturated fluid

A term used to describe a solution where an undissolved solute is present. This is useful in saltwater muds where the undersaturated flued can allow salt to leach into the mud, preventing the hole from closing in on the drilling assembly.

When used to describe moisture in the air, this term refers to humidity less than 100%.


Refers to the quantities of petroleum that are estimated to be contained within accumulations that have not yet been tested by drilling.

Uniaxial compressive strength

This term is a type of measurement used to illustrate a material’s strength. The uniaxial compressive strength is sometimes abbreviated to UCS and describes the maximum axial compressive stress that a right-cylindrical sample of material can endure before failing.

Sometimes referred to as ‘unconfined compressive strength’.

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Refers to a copolymer of vinyl acetate (ethylenic polymer) and anhydrous maleic acid (a di-hydroxy acid) that usually has a high molecular weight. Because of this, it’s often used as a flocculant (a substance which promote the clumping of fine particles) or bentonite extender (used to Prevent solids separation/reduce free water)

Vantage POB

Refers to a shared service to oil and gas operators (by LOGIC) for personnel and certification tracking at onshore and offshore installations in the United Kingdom.

Before the year 2000, each operator had an independent system.

Vapor extraction (vapex)

A non-thermal heavy oil manufacturing method that consists of a solvent vapor being used to reduce the viscosity of heavy oil. The solvent is injected into the heavy oil and subsequently expands and dilutes. The diluted heavy oil will then drain to the lover horizontal well.

Velocity correction factor

The Velocity Correction factor links the velocity of single-phase liquid flow measured in the centre of a pipe with the average velocity across the pipe.


Refers to ethylenediaminetetraacetic acid which is the substance used to titrate for calcium and magnesium ions in water samples. It’s also known as titraver or EDTA.

Viscous oil

Crude oil with high viscosity (typically above 10 cp), and high specific gravity. Heavy oils tend to have low hydrogen-to-carbon ratios, high asphaltene, sulfur, nitrogen, heavy-metal content and higher acid numbers.


Viscosity is a measurement of a fluid’s resistance to flow and is sometimes abbreviated to ‘Vis’.


Stands for ‘Vertical Seismic Profile’ and is a technique used to record seismic waves directly at a borehole which enables seismic two-way travel time reflectors to be accurately correlated with formation depths encountered by the well.

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Wait On Cement (WOC)

This abbreviation refers to suspending drilling operations so cement slurries can harden and solidify. This allows the slurry to develop compressive strength so small cracks or fluid pathways do not form. The WOC time can range from a few hours up to several days and the drilling crew will usually use this time for maintenance.

Wall Sticking

Refers to a condition where the drill string cannot move along the axis of the wellbore. This is sometimes known as ‘Differential Sticking’. This is often described as the greatest drilling problem in terms of financial costs and time lost and it occurs when high-contact forces caused by low reservoir pressures, high wellbore pressures, or both, are exerted over a large area of the drillstring.

Wellbore Orientation

Wellbore Orientation describes the direction of the wellbore in terms of inclination and azimuth. Inclination is the vertical angle and Azimuth is the horizontal angle.


Refers to the borehole, drilled hole, openhole or uncased portion of the well.


The system of valves, spools and assorted adapters that provide pressure control for a production well.

Wiper Plug

A Wiper Plug, (sometimes referred to as a cementing plug) is a rubber plug used to separate the cement slurry from other fluids. This reduces contamination and maintains predictable slurry performance.

Wireline Log

Refers to the continuous measurement of formation properties. Electrically powered instruments are used to gather information about the formation so decisions can be made about drilling operations.


This term refers to the stimulation or repair of an existing production well. The purpose of this is to restore or prolong the production of hydrocarbons.


An openhole section or an enlarged region of a wellbore. A Washout is usually larger than the size of the drillbit and can be caused by excessive bit jet velocity, soft formations, in-situ rock stresses, mechanical damage amongst other reasons. They can become more severe with time but using an appropriate mud time can minimize them.

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Extended-reach lateral; a well with a horizontal lateral of approximately 9,500 feet.

Xmas tree

An assembly of valves, casing spools, and fittings on the top of the casing which control the production rate of oil.

X-Ray Diffraction (XRD)

X-Ray Diffraction (XRD) is a standard service for any mineral identification and quantification in the oil and gas exploration industry.

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Can be used as a drilling term to refer to the volume occupied by one bag of dry cement after mixing with water and additives to form a slurry. Or the specified minimum yield strength of steel used in a pipe.

It can also be used when discussing Drilling Fluids to specify the quality of a clay corresponding to the number of barrels of 30-cP viscosity mud that one tonne would produce.

Yield stress

The stress that must be applied to a material to make it begin to flow (or to yield).

Yield point

A geology term used to describe the elastic limit of a material. When the elastic limit is surpassed by an applied stress, permanent distortion occurs.

Or sometimes used as a Drilling Fluids term to describe the parameter of the Bingham plastic model which is a two-parameter rheological model widely used to describe flow traits of muds.


A production term used to describe the part of a gate valve that operates as a spacer between the bonnet and the operator.

Young-Laplace equation

A nonlinear partial differential equation describing the pressure difference across an interface between two fluids at a static, curved interface, used to define the capillary pressure.

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Zinc Basic Carbonate

A neutral double salt of zinc carbonate and zinc hydroxide used as for water-based drilling fluids.

Zinc Bromide

An acidic salt, ZnBr2, used to prepare dense, solids-free brine for workover operations and well completion.

Zinc Carbonate

A neutral zinc salt, ZnCO3, used as a sulphide scavenger in water-base muds which is less soluble than zinc basic carbonate.

Zinc Chloride

An acidic salt, ZnCl2, used as one of the standard saturated salt solutions for calibration of the electrohygrometer. Zinc chloride is used in saltwater mud because the chloride salt does not cause detrimental effects on mud performance.

Zinc Oxide

Another sulphide scavenger, ZnO, which has a very weak base. This is used in oil-based or synthetic-based muds.

Zip Collars

Sometimes referred to Zip Groove, is used to describe drill collars that have been manufactured with a reduced diameter so that they may be more easily handled with open-and-close elevators.

Zero-Zero Gels

Zero-zero gels mud allows barite and cuttings to settle. The gel strength is considered to be very low with both values near zero when measured according to standardized test procedures.

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