Accrete Petroleum Limited


Our mission is to help our clients make distinctive and substantial improvements in their performance, so we believe that this glossary for upstream oil and gas industry terms will help them to succeed in their work. We believe we will be successful if our clients are successful. 



To stop work on a well or field which is non-productive and reached its economic limit.


The act or process of reducing the intensity of pollution.(2) The use of some method of abating pollution.

Abnormal Pressure

The term is usually associated with higher than normal pressure, increased complexity for the well designer and an increased risk of well control problems. Pressure gradients more than around 10 pounds per gallon equivalent fluid density are considered abnormal.


An accumulation is one or more pools or reservoirs of petroleum that make up an individual production unit and is defined by trap, charge, and reservoir characteristics. Two types of accumulations are recognized, conventional and continuous.


It is a well stimulation technique whereby acid is injected into the reservoir rock to improve reservoir permeability and so increase the flow from the reservoir.

Adjustable Choke (ADJCK)

A valve, located on or near the Christmas tree, that is used to control the production of fluid from a well. Opening or closing the variable valve influences the rate and pressure at which production fluids progress to the facilities.


The amount of oil and/or natural gas a well or a leasehold is permitted to produce under pro ration orders of a state regulatory body.

Amplitude Anomaly

An abrupt increase in seismic amplitude that can indicate the presence of hydrocarbons. Amplitude anomalies that indicate the presence of hydrocarbons can result from sudden changes in acoustic impedance, such as when a gas sand underlies a shale, and in that case, the term is used synonymously with hydrocarbon indicator.


The space between two concentric lengths of pipe or between pipe and the hole in which it is located.

Geological Term: A fold in layered rocks originating below the surface in the form of an elongated dome. Anticlines make excellent drilling prospects since any oil in the deposit will naturally rise to the highest point of the domed structure because oil always floats on top of the water.

Anticlinal Trap

A type of structural hydrocarbon trap whose closure is controlled by the presence of an anticline.

Appraisal Well

Well drilled after the discovery of oil or gas to establish the limits of the reservoir, the productivity of wells in it and the properties of the oil or gas. This well can be a production well in the development phase.

To test a metal or an oil for purity or quality.

Assessment Unit (AU)

A mappable volume of rock within a total petroleum system that encompasses accumulations (discovered and undiscovered) that share similar geologic traits and socio-economic factors. Accumulations within an assessment unit should constitute a sufficiently homogeneous population such that the chosen methodology of resource assessment is applicable. A total petroleum system might equate to a single assessment unit. If necessary, a total petroleum system can be subdivided into two or more assessment units in order that each unit is sufficiently homogeneous to assess individually. An assessment unit may be identified as conventional, if it contains conventional accumulations, or as continuous, if it contains continuous accumulations.

Assessment Unit Probability

The assessment unit probability, expressed as a decimal fraction, represents the likelihood that, in a given assessment unit, at least one undiscovered accumulation of a selected minimum size exists that has the potential for its volume to be added to proved reserves in a given time frame. The assessment unit probability is the product of the probabilities of the three geologic attributes (charge, rocks, and timing) and the probability of access.

Associated gas 

Natural gas found in association with oil in a reservoir, either dissolved in the oil or as a cap above the oil.


American Petroleum Institute

API County Code

An indicator developed by the American Petroleum Institute (API) to identify areas such as counties and other subdivision areas identified within state boundaries. Defined by API Bulletin D12A, as amended. This code becomes a part of the API Well Number.

API gravity

The universally accepted scale adopted by the American Petroleum Institute for expressing the specific gravity of oils. As the API of the oil increase it means it has more quality and more lighter.

API State Code

The indicator assigned to a state, as defined in API Bulletin D12A, as amended. This code is a part of the API Well Number (The Api State Code for Colorado is 05).

API Well Number

A well identifier assigned as defined in API (American Petroleum Institute)Bulletin D12A, as amended. The API Well Numbers are assigned by the appropriate state or federal regulatory agency.

Authority for Expenditure (“AFE”)

A budgetary document to list estimated expenses of drilling a well to a specified depth, casing point or geological objective, and then either completing or abandoning the well. Such expenses may include excavation and surface site preparation, the daily rental rate of a drilling rig, costs of fuel, drill pipe, bits, casing, cement and logging, and coring and testing of the well, among others. This estimate of expenses is provided to partners for approval before commencement of drilling or subsequent operations. Failure to approve an AFE may result in delay or cancellation of the proposed drilling project or subsequent operation.


Back Off (“BO”)

To unscrew drillstring components downhole. The drillstring, including drillpipe and the bottomhole assembly, are coupled by various thread forms known as connections or tool joints. Often when a drillstring becomes stuck it is necessary to “back off” the string as deep as possible to recover as much of the drillstring as possible. To facilitate the fishing or recovery operation, the back off is usually accomplished by applying reverse torque and detonating an explosive charge inside a selected threaded connection.


The right to receive a reversionary interest at some future time, upon fulfillment of contractually specified conditions. This clause allows a non participating partner to reserve the option to participate in a well after it has produced enough to pay the operator’s expenses of drilling and completing that well. This clause is typically used in participation agreements to convert the overriding royalty interest of a non participating partner (the Generator) into a working interest upon payout of the well. When the election to convert the overriding royalty interest to working interest takes place, it is known as a “back-in after payout.”


A cylindrical, bucket-like piece of equipment used to evacuate its liquid content in, or remove mud and rock cuttings from, the hole or wellbore.


(bbl: barrel; MMbbls: million barrels) a unit of measure for oil and petroleum products equal to 42 US gallons or 35 imperial gallons.

Barrels of Condensate Per Day (“BCPD”)

A common unit of measurement for the daily volume of condensate produced by a well. The volume of a barrel is equivalent to 42 U.S. gallons.

Barrels of Oil Equivalent (BOE)

A unit of petroleum volume in which the gas portion is expressed in terms of its energy equivalent in barrels of oil. For this assessment, 6,000 cubic feet of gas equals 1 barrel of oil equivalent (BOE).

Barrels of Water Per Day (“BWPD”)

A common unit of measurement for the daily volume of water produced by a well. The volume of a barrel is equivalent to 42 U.S. gallons.

Basement Rock

Igneous or metamorphic rock lying below sedimentary formation in the earth’s crust. Basement rock does not contain petroleum deposits.

Basic Sediment and Water (“BS&W”)

A combination of impurities and water which is often produced with crude oil. BS&W is heavier than oil and will settle to the bottom of a tank.


A depression in the earth’s crust in which sedimentary materials have accumulated. Such a basin
may contain oil or gas fields.

If a well drills through several pay zones and is completed in the deepest productive reservoir, casing
is set all the way down to the producing zone. Viewed from (a perspective) inside the borehole,
in the shallower pay zones up the hole are behind the casing.

The pressure of the reservoir or formation at the bottom of the hole. A decline in pressure indicates some depletion of the reservoir.

A measured amount in which crude oil and refined product shipments are sent through a pipeline.

Essentially a “squirt” of product that travels at one time along a pipeline.

Batching Sequence
The order in which squirts of petroleum product are sent through a pipeline.

Holding facility that stores and/or processes crude oil.

Billion cubic feet. Measures petroleum.

The tool used to crush or cut rock. Everything on a drilling rig directly or indirectly assists the bit in crushing or cutting the rock.

Heavy oil or petroleum in semi-solid or solid forms.

Blind Ram

A thick, heavy steel component of a conventional ram blowout preventer. The blind ram has no space for pipe and is instead blanked off to be able to close over a well that does not contain a drillstring. It may be loosely thought of as the sliding gate on a gate valve.

Applies to an area of land – main subdivision used for exploration and production acreage.


Uncontrolled flow of formation fluids from the well during the drilling stage.

Blow-out Preventer (BOP)

It is a well control equipment fitted to the top of the casing to prevent blow-outs and control the well.


Barrels of oil equivalent per day


Barrels of oil per day


The hole itself, including the openhole or uncased portion of the well. Borehole may refer to the inside diameter of the hole wall, the rock face that bounds the drilled hole.

Bottomhole Assembly (“BHA”)

The lower portion of the drillstring, consisting of (from the bottom up) the bit, bit sub, a mud motor (in certain cases), stabilizers, drill collars, heavyweight drillpipe, jarring devices (“jar”) and crossovers for various thread forms. The bottomhole assembly can also include directional drilling and measuring equipment, measurements-while drilling tools, logging-while-drilling tools and other specialized devices.

Bottomhole Location (“BHL”)

The actual location of a hole or wellbore at its deepest point.

Bottomhole Pressure (“BHP”)

The pressure at or near the depth of the producing formation.


Pertaining to the drilling mud and cuttings that are calculated or measured to come from the bottom of the hole since the start of circulation.

Break Circulation

To establish circulation of drilling fluids after a period of static conditions. Circulation may resume after a short break, such as taking a survey or making a mousehole connection, or after a prolonged interruption, such as after a round trip.

Break Out

To unscrew drillstring components, which are coupled by various thread forms known as connections, including tool joints and other threaded connections.


A wellbore obstruction caused by a buildup of material such as scale, wellbore fill or cuttings that can restrict borehole access or, in severe cases, eventually close the borehole.


The accumulation or buildup of material, such as sand or scale, within a wellbore, insofar as the flow of fluids or passage of tools or downhole equipment is severely obstructed. In extreme cases, the wellbore can become completely plugged or bridged-off, requiring some remedial action before normal production can be resumed.

Bridge Plug (“BP”)

A downhole tool that is located and set to isolate the lower part of the wellbore. Bridge plugs may be permanent or retrievable, enabling the lower wellbore to be permanently sealed from production or temporarily isolated from a treatment conducted on an upper zone.

Bright Spot

A seismic amplitude anomaly or high amplitude that can indicate the presence of hydrocarbons. Bright spots result from large changes in acoustic impedance and tuning effects, such as when a gas sand underlies a shale, but can also be caused by phenomena other than the presence of hydrocarbons, such as a change in lithology. The term is often used synonymously with hydrocarbon indicator.

British Thermal Unit (BTU)
The amount of heat required to increase the temperature of a pound of water 1 degree Fahrenheit. A BTU is the common measure of heating value for different fuels. Prices of different fuels and their units of measure (dollars per barrel of crude, dollars per ton of coal, cents per gallon of gasoline, cents per thousand cubic feet of natural gas) can be easily compared when expressed as dollars and cents per million BTUs.


To forcibly pump fluids into a formation, usually formation fluids that have entered the wellbore during a well control event.

Bump the Plug

To observe the increase in pump pressure indicating that the top cement plug has been placed on the bottom plug or landing collar. Bumping the plug concludes the cementing operation.

Bunker C Fuel Oil
Heavy fuel used for ships. Generally refers to a No. 6 grade of. residual fuel oil which has had limited refining.


Cap Rock

A relatively impermeable rock, commonly shale, anhydrite or salt, that forms a barrier or seal above and around reservoir rock so that fluids cannot migrate beyond the reservoir. It is often found on top of salt domes.

Cap the Well

To regain control of a blowout well by installing and closing a valve on the wellhead.

Carried Working Interest

A working interest generally paid in consideration for work related to the prospect. This interest is paid, or carried, for the drilling and/or completion costs as specified in the contract between the parties, by another working interest owner typically until casing point is reached, or through the tanks, meaning through completion of the well, as agreed upon contractually.
Cased Hole

A wellbore lined with a string of casing or liner. Although the term can apply to any hole section, it is often used to describe techniques and practices applied after a casing or liner has been set across the reservoir zone, such as cased-hole logging or cased-hole testing.


Lining a drilled hole with steel pipe. The pipe is cemented in place to prevent the hole caving in.

Casing head Gas
Gas present in an oil well that is removed when it flows to the surface at the well’s casing.

Casing Joint

A length of steel pipe, generally around 40 feet long with a threaded connection at each end. Casing joints are assembled to form a casing string of the correct length and specification for the hole in which it is installed.
Casing Patch

A downhole assembly or tool system used in the remedial repair of casing damage, corrosion or leaks. In some cases, such as in depleted wells, a casing patch may be an economic means of safely deepening a well.

Casing Point

The point at which a well has been drilled to the desired depth and the owners must decide whether or not to place production pipe, called casing, in the hole and proceed to complete and equip the well for production.

Casing Shoe

The bottom of the casing string, including the cement around it, or the equipment run at the bottom of the casing string.

Casing Shoe Test or Testing the Shoe

A pressure test applied to the formation directly below a casing shoe. The test is generally conducted soon after drilling resumes after an intermediate casing string has been set. The purpose of the test is to determine the maximum pressures that may be safely applied without the risk of formation breakdown.


A subdivision or area within an assessment unit having dimensions related to the drainage areas of wells (not to be confused with finite-element cells). Three categories of cells are recognized, cells tested by drilling, untested cells, and untested cells having potential to provide additions to reserves within the forecast span of the assessment. A continuous assessment unit is a collection of petroleum-containing cells.

Cement Bond Log (“CBL“)

A representation of the integrity of the cement job, especially whether the cement is adhering solidly to the outside of the casing.

Cement Plug

A balanced plug of cement slurry placed in the hole or wellbore. Cement plugs are used for a variety of applications including hydraulic isolation, provision of a secure platform, and in window-milling operations for sidetracking a new hole or wellbore.

Cement Squeeze or Squeeze Job

A remedial cementing operation designed to force cement into leak paths in wellbore tubulars. The required squeeze pressure is achieved by carefully controlling pump pressure. Squeeze cementing operations may be performed to repair poor primary cement jobs, isolate perforations or repair damaged casing or liner.

Centrifugal pump
A rotating pump, like a large screw, used for pushing large volumes of oil and gas through pipelines.


The condition in which cement flows in a channel only on some sides of the casing or borehole annulus, and thus does not provide adequate hydraulic isolation in all radial azimuths.


A device incorporating an orifice that is used to control fluid flow rate or downstream system pressure. Chokes are available in several configurations for both fixed and adjustable modes of operation. Adjustable chokes enable the fluid flow and pressure parameters to be changed to suit process or production requirements. Fixed chokes do not provide this flexibility, although they are more resistant to erosion under prolonged operation or production of abrasive fluids.

Christmas tree

The arrangement of pipes and valves at the wellhead which controls the flow of oil and gas and prevents blowouts.

Circulate or Circulation (“Circ”)

To pump drilling fluid through the whole active fluid system. The round trip made by drilling fluid; down through the drillstring, up on the outside of the drillstring (between the drillpipe and the walls of the hole), through the mud system and then back down the drillstring again.

Circulate and Condition Mud (“C&CM”)

The operation of circulating the drilling fluids to either increase or decrease the mud weight.


A period of controlled production, generally following the perforating of a zone or a stimulation treatment, during which time completion/treatment fluids return from the reservoir formation.

Closed Mud System or Closed Loop System

A mud and solids-control system in which the only discarded waste is moist, drilled-up rock materials. Such systems are used for drilling wells in environmentally sensitive areas.


Compressed Natural Gas

Coiled Tubing

A continuous, jointless hollow steel cylinder that is stored on a reel and can be uncoiled or coiled repeatedly as required; coiled tubing is increasingly being used in well completion and servicing instead of traditional tubing, which is made up of joined sections of pipe.

Company Man

The representative of the oil company or operator on a drilling location, who is responsible for the safety and efficiency of the project.

The final installation of permanent equipment for the production of oil or gas.

Completion Fluid

A solids-free liquid used to “complete” an oil and/or natural gas well. This fluid is placed in the wellbore to facilitate final operations before initiation of production, such as setting screens, production liners, packers, downhole valves or shooting perforations into the producing zone.
Composite Log

A single log created by splicing together two logs of the same type run at different times in the well; or by splicing two different types of log run at the same time.

Composite Total Petroleum System

A mappable entity encompassing all or a portion of two or more total petroleum systems. The concept of composite total petroleum systems is applied when accumulations within an assessment unit are assumed to be charged by more than one source rock.

Compression Set Packer

A type of downhole packer that is made active or set by applying compressive force to the packer assembly.


A device that raises the pressure of air or natural gas. A compressor normally uses positive displacement to compress the natural gas to higher pressures so that the gas can flow into pipelines and other facilities.

Compressor station
Stations located every 60-80 km along a gas pipeline which re-compress gas to ensure an even flow.

A defined license area granted to a company for the exploration of oil and/or gas under specific terms and conditions for a fixed period of time.

Any mixture of relatively light hydrocarbons which remain liquid at normal temperature and pressure. Condensate generally appears when gas is drawn from a well and its temperature and pressure change sufficiently for some of it to become liquid petroleum.

Condensate Liquids

Hydrocarbons that are in the gaseous phase at reservoir conditions but condense into liquid as they travel up the wellbore and reach separator conditions.

Conductor Pipe or Conductor Casing

The casing string that is usually put into the borehole first to prevent the sides of the hole from caving into the borehole. This casing, sometimes called drive pipe, is generally a short length and is sometimes driven into the ground.


The change in oil-water or gas-oil contact profiles as a result of drawdown pressures during production. Coning occurs in vertical or slightly deviated wells and is affected by the characteristics of the fluids involved and the ratio of horizontal to vertical permeability. Coning can also result from producing a well at high rate of production.

Continuous Accumulation

A petroleum accumulation that is pervasive throughout a large area, that is not significantly affected by hydrodynamic influences, and for which the chosen methodology for assessment of sizes and number of discrete accumulations is not appropriate. Continuous accumulations lack well-defined down-dip water contacts. The terms continuous accumulation and continuous-type accumulation are used interchangeably.

Conventional Accumulation

A discrete accumulation commonly bounded by a down-dip water contact and significantly affected by the buoyancy of petroleum in water. This geologic definition does not involve factors such as water depth, regulatory status, or engineering techniques

Conventional crude
Liquid petroleum that is capable of flowing naturally without any processing.


A continuous cylinder of rock, usually from 5 to 10 centimeters in diameter, cut from the bottom of a borehole as a sample of an underground formation. (See “Sidewall Core”)

Cost Depletion

Recovery of one’s tax basis in a producing oil or gas well by deducting basis proportionately over the producing life of the well. See also Percentage Depletion.


Central Processing Facility

Crown lands
Government owned properties.

Crude Oil
A mixture of hydrocarbons that exists as a liquid in natural underground reservoirs and remains liquid at atmospheric pressure after passing through surface separating facilities. Crude is the raw material which is refined into gasoline, heating oil, jet fuel, propane, petrochemicals, and other products.

Cubic foot
The amount of gas required to fill a volume of one cubic foot.

Cubic feet per day (cfpd)
The number of cubic feet of natural gas produced from a well over a 24 hour period, normally an average figure from a longer period of time.

Cumulative Petroleum Production

Reported cumulative volume of petroleum that has been produced. Cumulative oil, cumulative gas, and cumulative production are sometimes used as abbreviated forms of this term.

Cushion Gas
The amount of gas required in a storage pool to maintain sufficient pressure to keep the working gas moving so it can be recovered.


Small pieces of rock that break away due to the action of the bit. Cuttings are screened out of the drilling mud system at the “shale shakers” and are monitored for composition, size, shape, color, texture, hydrocarbon content and other properties.


Day Rate

The daily cost to the operator of renting the drilling rig and the associated costs of personnel and routine supplies. This cost may or may not include fuel, and does not include capital goods, such as casing and wellheads, or special services, such as logging or cementing. In most of the world, the day rate represents roughly half of the cost of the well. Similarly, the total daily cost to drill a well (spread rate) is roughly double what the rig day rate amount is.

Daisy chain
Term refers to the “chain” of linked sales and transfers by which a cargo of oil or oil products is sold many times before being delivered to the customer.


Removal of production equipment and facilities from depleted oil fields

Delay Rental

Consideration paid to the lessor by a lessee to extend the terms of an oil, gas and mineral lease in the absence of operations and/or production that is contractually required to hold the lease. This consideration is usually required to be paid on or before the anniversary date of the oil, gas and mineral lease during its primary term, and typically extends the lease for an additional year. Nonpayment of the delay rental without production or commencement of operations will result in abandonment of the lease after its primary term has expired.

Deliverability Test

Tests in an oil and/or gas well to determine its flow capacity at specific conditions of reservoir and flowing pressures. The absolute open flow potential can be obtained from these tests, and then the inflow performance relationship can be generated. A deliver ability test also is called a productivity test.

The gravity of crude oil. Density is measured in kilograms of large, carbon-rich molecules per cubic metre or degrees on the American Petroleum Institute (API) gravity scale.


The drop in reservoir pressure or hydrocarbon reserves resulting from production of reservoir fluids.


An accumulation of oil and/or natural gas which is capable of commercial production.

Steel structure mounted over the bore hole to support the drill pipe and other equipment which is lowered and raised during drilling operations.

Development well

A well drilled within the proved area of an oil or gas reservoir to the depth of a stratigraphic horizon known to be productive

The angle at which a hole or wellbore diverges from vertical. Wells can deviate from vertical because of the dips in the beds being drilled through. Wells can also be deliberately deviated with the use of a whipstock or other steering mechanism. Wells are often deviated or turned to a horizontal direction to increase exposure to producing zones, intersect a larger number of fractures, or to follow a complex


domestic gas supply obligation

Diesel Fuel
Distillate fuel oil used in compression-ignition engines. It is similar to home heating oil, but must meet a cetane number specification of 40 or more.


The magnitude of the inclination of a plane from horizontal. True, or maximum, dip is measured perpendicular to strike. Apparent dip is measured in a direction other than perpendicular to strike.

Directional Drilling

It is a technique used to control the direction and deviation of a wellbore to a predetermined subsurface location.

Division Order

An agreement between the operator and net revenue interest owner in which the parties specify the fractional type of interest attributed to the revenue interest owner by the operator after an examination of title.


Any of various viscous materials used on pipe or tubing threads as a lubricant, and to prevent corrosion; a tar base coating for pipelines to prevent corrosion.


Located down the slope of a dipping plane or surface. In a dipping (not flat-lying) hydrocarbon reservoir that contains natural gas, oil and water, the natural gas is updip, the gas-oil contact is downdip from the natural gas, and the oil-water contact is still farther downdip.

Downhole Equipment 

A term used to describe tools, equipment, and instruments used in the wellbore, or conditions or techniques applying to the wellbore


Refining of crude oil and the marketing and distribution of oil products that occur after refining, as opposed to upstream


The collective name for the hoisting drum, cable, shaft, clutches, power take off, brakes, and other machinery used on a drilling rig. Drawworks are located on one side of the derrick floor, and serve as a power-control center for the hoisting gear and rotary elements of the drillstring.


It is a cutting tool attached to the drill-string used to make the wellbore.

Drill Collars (“DC”)

A component of a drillstring that provides weight on the bit for drilling.


One who operates a drilling rig; the person in charge of drilling operations and who supervises the drilling crew.

Drilling Mud or Fluid

Drilling fluids are added to the wellbore to facilitate the drilling process by suspending cuttings, controlling pressure, stabilizing exposed rock, providing buoyancy, and cooling and lubricating.

Drilling Procedure

The engineering plan for constructing the wellbore. The plan includes well geometries, casing programs, mud considerations, well control concerns, initial bit selections, offset well information, pore pressure estimations, economics and special procedures that may be needed during the well. Although drilling procedures are carefully developed, they are subject to change if drilling conditions dictate.

Drillpipe (“DP”)

Steel pipe screwed together and used to carry and rotate the drilling tools in a well, and to permit the circulation of drilling fluid. Drillpipe comes in lengths of approximately 30 feet. As the well is drilled deeper, they must constantly disconnect the drillstring, thread on another 30 foot section and then drill deeper.

Dry and Abandon (“D&A”)

A well which is drilled and did not encounter oil and/or natural gas in commercial quantities and is subsequently abandoned.

Dry Gas

Natural gas from a well that is free of liquid hydrocarbons, or gas that has been treated to remove all liquids; pipeline gas.

Dry hole

A wellbore that has not encountered hydrocarbons in economically producible quantities

Drill string

Steel pipes roughly 10m long joined together to form single pipe from the drill bit to the drilling platform. It is rotated during drilling and is also the conduit for the drilling mud.

Dual Completion

A single wellbore having tubulars and equipment that enable production from two segregated zones. In most cases, two tubing strings will be used to provide the necessary level of control and safety for the fluids from both zones. However, in some simple dual completions, the second or upper zone is produced up the tubing-casing annulus.



Abbreviation for exploration and appraisal


Exploration and production. The “upstream” sector of the oil and gas industry

Electrical Log (“ELOG”)

An electrical survey of an uncased hole which reflects the degree of resistance of the rock strata to electric current. From the results of the survey, geologist are able to determine the nature of the rock penetrated in the hole and some indications of its permeability.


hinged mechanism that may be closed around drillpipe or other drillstring components to facilitate lowering them into the hole or lifting them out of the hole.


Escravos-Lagos Pipeline System


Abbreviation of Enhanced Oil Recovery methods which used to increase the recovery from the oil reservoirs.


Engineering, Procurement and Construction

Estimated Ultimate Recovery (EUR)

The total expected recoverable volume of oil, gas, and natural gas liquids production from a well, lease, or field under present economic and engineering conditions; synonymous with total recovery


An appearance of seismic data as a diffraction, reflection, refraction or other similar feature produced by an arrival of seismic energy. An “event” can be a single wiggle within a trace, or a consistent lining up of several wiggles over several traces. An event in a seismic section can represent a geologic interface, such as a fault, unconformity or change in lithology.

Expendable Gun

A perforating gun assembly that disintegrates upon firing, thereby reducing the volume and dimensions of retrieved components. Expendable guns are typically used where wellbore restrictions allow only limited access, as in through-tubing applications. The distortion caused to the gun assembly during firing would typically prevent recovery of a conventional gun design through the limited clearances. The expendable gun assembly breaks into small pieces that drop to the bottom of the well, leaving only a relatively small sub-assembly that is easily recovered to surface.

Expendable Plug

A temporary plug, inserted in the completion assembly before it is run, to enable pressure testing of the completed string. With the operation complete, the expendable plug can be pumped out of the assembly, thereby avoiding a separate retrieval run.

Exploratory well
A well in an area where petroleum has not been previously found or one targeted for formations above or below known reservoirs.


Farm in

When a company acquires an interest in a block by taking over all or part of the financial commitment for drilling an exploration well.

The land owner gives a percentage of his land or a portion of his working interest in a well in order to allow an outside party to drill or explore on his property. This generally reduces risk as capital is provided by the company farming-in.

A geological structure consisting of a fracture in the rock along which there has been an observable amount of displacement.

Fault Trap

A type of structural hydrocarbon trap in which closure is controlled by the presence of at least one fault surface.

The supply of crude oil, natural gas liquids, or natural gas to a refinery or petrochemical plant or the supply of some refined fraction of intermediate product to some other manufacturing process.


A geographical area under which an oil or gas reservoir lies.

Field Growth

The increases in known petroleum volume that commonly occur as oil and gas fields are developed and produced; synonymous with reserve growth

Fish (“Fsh”)

Anything left in a hole or wellbore. It does not matter whether “the fish” consists of junk metal, a hand tool, a length of drillpipe or drill collars, or an expensive mud motor and directional drilling package. Once the component is lost, it is properly referred to as simply “the fish.” Typically, anything put into the hole is accurately measured and sketched, so that appropriate fishing tools can be selected if the item must be fished out of the hole.


Retrieving objects from the borehole, such as a broken drillstring, or tools.

Fishing Tool

Fishing Tool -A general term for special mechanical devices used to aid the recovery of equipment lost downhole. These devices generally fall into four classes: diagnostic, inside  grappling, outside grappling, and force intensifiers or jars. Diagnostic devices may range from a  simple impression block  made in a soft metal, usually lead, that is dropped rapidly onto the top of the fish so  that upon inspection at the surface, the crew may be able to custom design a tool to facilitate attachment to and   removal of the fish. Other diagnostic tools may include electronic instruments and even downhole sonic or visual-bandwidth cameras. Inside grappling devices, usually called spears, generally  have a tapered and threaded profile, enabling the crew to first guide the tool into the top of the  fish, and then thread the fishing tool into the top of the fish so that recovery may be attempted. Outside grappling devices, usually called “overshots” are fitted with threads or another shape that “swallows” the fish and does not release it as t is pulled out of the hole. Overshots are also fitted with a crude
i drilling surface at the bottom, so that the overshot may be lightly drilled over the fish, sometimes to remove rock or metallic junk that may be part of the sticking mechanism. Jars are mechanical downhole hammers, which enable the crew to deliver high-impact loads to the fish, far more than what could be applied in a quasi-static pull from the surface.

The controlled and safe burning of gas which cannot be used for commercial or technical reasons. This usually occurs at the point of production, and during processing.

Flowing Tubing Pressure (“FTP”)

The pressure on the tubing as a well flows oil and/or natural gas.

Flowing Well

A well capable of producing oil by its own energy, without the aid of a pump or other means.


A surface pipeline carrying oil, natural gas or water that connects the Christmas tree to a manifold or to production facilities, such as a heater-treater and separator.

Fluid Level 

The depth, or distance from surface, that the fluid in a well incapable of natural flow will reach under static conditions.


Fisheries Legacy Trust Company; formed in 2007 by Oil & Gas UK, Scottish Fishermen’s Federation (SFF) and National Federation of Fishermen’s Organisations (NFFO) to enhance the safety of fishermen by ensuring the provision in perpetuity of information relating to oil and as seabed structures and equipment in UK waters.

Forecast Span

A specified future time span in which petroleum accumulations have the potential to provide additions

to reserves. A 30-year forecast span is used in the USGS assessments and affects (1) the minimum undiscovered accumulation size, (2) the number of years in the future that reserve growth is estimated, (3) economic assessments, (4) the accumulations that are chosen to be considered, and (5) the risking structure as represented by access risk.


A general term for the rock around the borehole. In the context of formation evaluation, the term refers
to the volume of rock seen by a measurement made in the borehole, as in a log or a well test.

Formation Damage

A general term to describe the reduction in permeability to the nearwellbore area of a reservoir formation.  There are several recognized damage mechanisms, such as the invasion of incompatible fluids swelling the formation clays, or fine solids from dirty fluids plugging the formation matrix.

Formation pressure

The pressure at the bottom of a well when it is shut in at the wellhead.

Formation water

Salt water underlying gas and oil in the formation.


Floating Production Storage Offloading

The process whereby saturated hydrocarbons from natural gas are separated into distinct parts or ‘ fractions” such as propane, butane, ethane,

Fuel Oil
Refined petroleum products used as a fuel for home heating and industrial and utility boilers. Fuel oil is divided into two broad categories, distillate fuel oil, also known as NO. 2 fuel, gasoil, or diesel fuel; and residual fuel oil, also known as No. 6 fuel, or outside the United States, just as fuel oil. No. 2 fuel is a light oil used for home heating, in compression ignition engines, and in light industrial applications. No. 6 oil is a heavy fuel used in large commercial, industrial, and electric utility boilers.


Gas Accumulation

An accumulation with a gas to oil ratio of 20,000 cubic feet/barrel or greater.

Gas in Gas Accumulations

Gas volumes in gas accumulations.

Gas in Oil Accumulations

Gas volumes in oil accumulations.

Gas cap

In a field containing both gas and oil, some gas will often collect at the top of the reservoir in a single deposit known as a gas cap.

Gas field

A field containing natural gas but no oil.

Gas injection

The process whereby separated associated gas is injected back into a reservoir for pressure maintenance

Gathering lines

Pipelines that move petroleum from wells to processing or transmission facilities.

Gas-to-Liquids (GTL)

The conversion of natural gas to a liquid

Sensors used in seismic surveys capable of detecting the velocity of energy waves.


Global Gas Flaring Reduction Partnership


The Nigerian Gas Master Plan

Gas to Oil Ratio (GOR)

Ratio of gas to oil (in cubic feet/barrel) in an accumulation. GOR is calculated using known gas and oil volumes at surface conditions.

Geologic Province

A USGS-defined area having characteristic dimensions of perhaps hundreds to thousands of kilometers encompassing a natural geologic entity (for example, sedimentary basin, thrust belt, delta) or some combination of contiguous geologic entities.

Grown Petroleum Volume

Known petroleum volume adjusted upward to account for future reserve growth. Thirty years of reserve growth is considered for the USGS assessments.


Heavy crude
with a gravity below 28 degrees API. Recovery generally involves an
application of heat and steam. Canadian pipelines generally require oil
to have a gravity of at least 21:2 degrees API. Heavier crudes must be
blended with condensate or NGLs to be shipped by pipeline

Horizontal drilling
Drilling at an angle instead
of straight down. This drilling technique permits the operator to
contact and intersect a larger portion of the petroleum producing
horizon than conventional vertical drilling techniques. It can increase
production rates and yield more hydrocarbons from a single area.


A compound containing only the elements hydrogen and carbon. May
exist as a solid, a liquid or a gas. The term is mainly used in a
catch-all sense for oil, gas and condensate.


Independent Producer

Term generally applies to a non-integrated oil or natural
gas company, usually active in only one or two sectors of the industry.
An independent marketer buys petroleum products from major or
independent refiners and resells them under his own brand name or buys
natural gas from producers and resells it. There are also independents
which are active exclusively either in oil or gas production or

Infill drilling

Drilling more wells into the same pool so that oil does not have to travel as far through the rock.

Injection well

A well used for injecting fluids into a formation in an attempt to
increase force the petroleum out of the rock more efficiently.

Integrated company

Indicates a firm that operates in both the upstream and downstream sectors (from exploration through refining and marketing).


International Oil Companies


Independent Power Plant



The lower section, or ‘legs’, of an offshore platform.

Jet Fuel
Kerosene-type; high-quality kerosene product used primarily as fuel for commercial turbojet and turboprop aircraft engines.

Joint venture (“JV”)
An investment undertaken by a consortium, usually with one member acting as the operator.


Known Petroleum Volume

The sum of cumulative production and remaining reserves as reported in the databases used in support of the assessment. Also called total recoverable volume (sometimes called ultimate recoverable reserves or estimated ultimate recovery).



A legal document conveying the right to drill for oil and gas, or the tract of land on which a lease has been obtained where the producing wells and production equipment are located.

Liquids to Gas Ratio (LGR)

Ratio of total petroleum liquids (including oil, condensate, and natural gas liquids) to gas (in barrels/million cubic feet) in a gas accumulation. The LGR is calculated using known petroleum liquids and gas volumes at surface conditions. This ratio is used to assess the liquid co-products associated with undiscovered gas in gas accumulations.

Lifting costs

The cost of producing oil from a well or lease known also as OPEX

Light crude
Oil with a gravity of 28 degrees API or higher. High-quality light crude has a gravity of 40 degrees or higher.

Liquefied natural gas (LNG)

Natural gas that has been liquefied for ease of transport by cooling the gas to -162-C. Natural gas has 600 times the volume of LNG.

Liquefied Petroleum Gas (LPG)
Propane, butane, or propane-butane mixtures derived from crude oil refining or natural gas fractionation. For convenience of transportation, these gases are liquefied through pressurization



Routine repairs needed throughout the life of a well, usually required more for oil than for gas wells.

A term broadly applied to those multinational oil companies ‘ which by virtue of size, age, or degree of integration are among the preeminent companies in the international petroleum industry.

Market capitalization
Calculated by multiplying the number of outstanding shares by the current stock price. This represents the market’s valuation of the company at that specific time.


Thousand cubic feet.

Strong smelling compounds of carbon, hydrogen, and sulphur found in gas and oil. Sometimes added to natural gas for safety reasons.

The principal constituent of natural gas.

Metric tonne

Equivalent to 1000 kilos, 2204.61 lbs; 7.5 barrels.

Middle Distillate
Hydrocarbons that are in the so-called “middle boiling range” of refinery distillation. Examples are heating oil; diesel fuels, and kerosene.


A term sometimes used to refer to those industry activities that fall between exploration and production (upstream) and refining and marketing (downstream). The term is most often applied to pipeline transportation of crude oil and natural gas.

Minimum Accumulation Size

The smallest accumulation size (volume of oil in oil accumulations or volume of gas in gas accumulations) that is considered in the assessment process for conventional accumulations.

Minimum Petroleum System

The mappable part of a total petroleum system for which the presence of essential elements has been proved by discoveries of petroleum shows, seeps, and accumulations.

Minimum Total Recovery per Cell

The smallest total recovery per cell (volume of oil or gas) that is considered in the assessment process for continuous accumulations.

One million British Thermal Units, one dekatherm. Approximately equal to a thousand cubic feet (Md) of natural gas.


Millions of cubic feet per day (of gas).


A mixture of base substance and additives used to lubricate the drill bit and to counteract the natural pressure of the formation.



A volatile, colorless product of petroleum distillation. Used primarily as a paint solvent, cleaning fluid, and blendstock in gasoline production.


One of the three basic hydrocarbon classifications found naturally in crude oil. Naphthenes are widely used as petrochemical feedstocks.

Natural Gas
A naturally occurring mixture of hydrocarbon and nonhydrocarbon gases found in porous rock formations. Its principal component is methane.

Natural Gas Liquids (NGL)
A general term for all liquid products separated from natural gas in a gas processing plant. NGLs include propane, butane, ethane, and natural gasoline.

Natural Gas Liquids to Gas Ratio (for oil accumulations)

Ratio of natural gas liquids to gas (in barrels/million cubic feet) in an oil accumulation, calculated using known natural gas liquids and gas volumes at surface conditions. This ratio is used to assess the natural gas liquids associated with undiscovered gas in oil accumulations.

The amount of money a company receives per barrel of oil equivalent produced, after subtracting operating costs, royalties, and general and administrative costs.

Net debt
Long-term debt plus working capital.

Net production
Petroleum production that is owned by a company, individual, trust, or foundation, less royalties and production due others.


Nigerian Gas Flare Commercialization Programme


Nigerian Liquefied Natural Gas Company Ltd


Nigerian National Petroleum Corporation

Non-associated Gas

Natural gas in a reservoir which contains no crude oil.



Crude oil or condensate

Oil Accumulation

An accumulation with a gas to oil ratio of less than 20,000 (in cubic feet/barrel).

Oil in Gas Accumulations

Oil volumes in gas accumulations. For this assessment, oil in gas accumulations was calculated along with other liquids rather than separately.

Oil field

A geographic area under which an oil reservoir lies.

Oil in place
The estimation of the real amount of oil in a reservoir.

Organization of Petroleum Exporting Countries.

The individual, company, trust, or foundation responsible for the operation of the project. It applies in either exploration, development, and production of an oil or gas well or lease.


Operating Expenditure.



Rock in which oil and gas are found in exploitable quantities.

The capacity of a reservoir rock to transmit fluids.

An intermediate chemical derived from petroleum, hydrocarbon liquids, or natural gas, such as ethylene, propylene, benzene, toluene, and xylene.

A natural mixture of hydrocarbons in gaseous, liquid, or solid form.

P&A (plugged and abandoned)

A depleted well or dry hole that has been (typically) filled with cement and marked, with all surface equipment removed.


the Petroleum Industry Bill


A joint programme involving the Government and the UK oil and gas industry: operators, contractors, suppliers, trade unions and SMEs, aiming to secure the long-term future of the industry in the UK.


An offshore structure that is permanently fixed to the seabed.


A set of known or postulated oil and gas accumulations sharing similar geologic, geographic, and temporal properties, such as source rock, migration pathway, timing, trapping mechanism, and hydrocarbon type. A play may differ from an assessment unit; an assessment unit can include one or more plays.

Pinnacle reef
A conical formation in the subsurface rocks where hydrocarbons may be trapped.

A pipe through which oil or natural gas is pumped between two points, either offshore or onshore.

A natural underground reservoir that either contains or appears to contain petroleum.

The amount of open space within a rock, similar to a sponge.

Possible reserves
An estimate of possible oil and/or gas reserves based on geological and engineering data from undrilled or untested areas.

Probable reserves
An estimate of oil and/or gas reserves based on penetrated structures, but needing more advanced confirmation to be classified as proven reserves.

The separation of oil, gas, and natural gas liquids and the removal of impurities.

Proven reserves
The quantity of oil and gas estimated to be recoverable from known fields under existing economic and operating conditions. Determined on the basis of drilling results, production, and historical trends.

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.

Produced water

The water extracted from the subsurface with oil and gas. It may include water from the reservoir, water that has been injected into the formation, and any chemicals added during the production/treatment process. Produced water is also called ‘brine’ (and may contain high mineral or salt content) or ‘formation water’. Some produced water is quite fresh and may be used for livestock watering or irrigation (where allowed by law).

Proven field

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


Raw natural gas

Natural gas containing impurities and unwanted substances that have to be removed.

Recoverable reserves

That proportion of the oil and/gas in a reservoir that can be removed using currently available techniques.

Recovery factor

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

Remaining Petroleum Reserves

Volume of petroleum in discovered accumulations that has not yet been produced. Remaining reserves is used as an abbreviated form of this term.

Reserve Growth

The increases in known petroleum volume that commonly occur as oil and gas accumulations are developed and produced; synonymous with field growth.

Riser (drilling)

A pipe between a seabed BOP and a floating drilling rig.

Riser (production)

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


Drill crew members who work on the derrick floor, screwing together the sections of drillpipe when running or pulling a drillstring.


Drill crew members who handle the loading and unloading of equipment and assist in general operations around the rig.

The completion for production of an existing well bore in another formation . Only applies were the formation being drilled into is different from the formation where the well was previously completed.

Recoverable reserves
The proportion of hydrocarbons that can be recovered from a reservoir using existing techniques.

A complex of facilities where crude oil is separated into light or heavy fractions which are then converted into usable products.

means proven reserves.

Reserve life index
The number of years it would take to deplete proven reserves at the current production rate.

Reserve replacement ratio
The quantity of added reserves for every barrel of oil equivalent produced.

Porous permeable rock containing petroleum.

Rich gas
Gas which is predominately methane but with a relatively high proportion of other hydrocarbons.

An interest in an oil and gas lease that gives the owner of the interest the right to receive a portion of the production from the leased acreage (or of the proceeds of the sale of production). Generally does not require the owner to pay any portion of the costs of drilling or operating the wells on the leased acreage. Royalties may be either landowner’s royalties, which are reserved by the owner ‘of the
leased acreage at the time the lease is granted, or overriding royalties, which are usually reserved by an owner of the leasehold in connection with a transfer to a subsequent owner.

Royalty holiday
Some jurisdictions or regulators grant royalty free wells in certain situations. For instance, In Alberta, the first 70,000 boe produced from a horizontal well are generally royalty fee.


Seismic: 2-D or 3-D
Using sound waves traveling through rock, the operator produces either two-dimensional or three-dimensional computer assisted pictures of the sedimentary structures underground. These Seismic tests show the subsurface structures and help determine where a drilling program might be most successful.

Solution gas
Natural gas which is dissolved in the crude oil within the reservoir.

Sour or Sweet Crude
Industry terms which denote the relative degree of a given crude oil’s sulfur content. Sour crude refers to those crudes with a comparatively high sulfur content, 0.5% by weight and above; sweet refers to those crudes with sulfur content of less than 0.5%.

Sour gas
Contain large amounts of hydrogen sulphides or sulphur. In order to become sweet gas, the sulphur must be removed. Hydrogen sulphide is extremely poisonous, almost instantly fatal if inhaled. This makes it difficult to transport without some processing.

Spot market
An international market in which oil or oil products are traded for immediate delivery at the current price.

The commencement of drilling operations.

Sweet Gas
Petroleum which contains little or no hydrogen sulphate and as a result requires little processing.

Sweet Spot

An area within a continuous accumulation where production characteristics are relatively more favorable than elsewhere.

A fold in layered rock in the form of a dip or bowl

Secondary recovery

Recovery of oil or gas from a reservoir by artificially maintaining or enhancing the reservoir pressure by injecting gas, water or other substances into the reservoir rock.


The process of separating liquid and gas hydrocarbons and water. This is typically accomplished in a pressure vessel at the surface, but newer technologies allow separation to occur in the wellbore under certain conditions.


A production hiatus during which the platform ceases to produce while essential maintenance work is undertaken.


Southern North Sea.


The operation of drilling the first part of a new well.

Standard contracts

Known formerly as CRINE contracts, standard contracts have been developed by the Standard Contracts Committee and are issued by LOGIC for use within the industry between clients and their contractors, simplifying procedures and saving costs.

Standard agreements

State-of-the-art solutions for oil and gas industry agreements and recommended for use by all UKCS licensees. They are user-friendly and easy to implement. In helping simplify operational and transactional procedures, they focus resources and save costs.

Step Change in Safety

The UK based partnership with the remit to make the UK the safest oil and gas exploration and production province in the world. It was founded in 1997 by the oil and gas industry trade associations with the aim of reducing the UK offshore oil and gas industry injury rate by 50%.

Subsurface Allocation

An allocation of potential additions to reserves to land entities based on subsurface ownership of mineral rights.

Surface Allocation

An allocation of potential additions to reserves to land entities based on surface ownership.

Suspended well

A well that has been capped off temporarily.


Tar sands

Mixture of sand, water, and heavy hydrocarbons, where the petroleum which can be extracted requires
expensive processing..

An onshore transit facility that receives and stores crude oil and products from offshore production
facilities via pipeline and/or tankers.

Tertiary Recovery
Enhanced recovery methods for the production of oil or gas. Enhanced recovery of crude oil requires a means for displacing oil from the reservoir rock, modifying the properties of the fluids in the reservoir and/or the reservoir rock to cause movement of oil in an efficient manner, and providing the energy and drive mechanism to force its flow to a production well. Chemicals or energy is injected as required for displacement and for the control of flow rate and flow pattern in the reservoir, and a fluid drive is

provided to force the oil toward a production well.


Trillion Cubic Feet (of gas).


The Trans Nigeria Pipeline Project


Second-in-command of a drilling crew under the drilling superintendent. Responsible for the day-to-day running of the rig and for ensuring that all the necessary equipment is available.


The superstructure of a platform.

Total Petroleum System (TPS)

A mappable entity encompassing genetically related petroleum that occurs in seeps, shows, and accumulations (discovered or undiscovered) which have been generated by a pod or by closely related pods of mature source rock, together with the essential mappable geologic elements (source, reservoir, seal, and overburden rocks) that controlled fundamental processes of generation, migration, entrapment, and preservation of petroleum.

Total Recovery

The total expected recoverable volume of oil, gas, and natural gas liquids production from a well, lease, or field under present economic and engineering conditions; synonymous with estimated ultimate recovery.


Underbalanced drilling

Occurs when the operator of the site uses specialized mud or gas while drilling to allow for formation fluids to rise to the surface and thus prevent damage to the prospective formation.

Undiscovered Petroleum Resources

Resources postulated from geologic information and theory to exist outside of known oil and gas accumulations.

Owners of adjoining properties pool reserves together to form a single producing unit in which each has an interest.


In the daisy chain of petroleum production, all the activities that occur from exploration through to production of raw product at the wellhead. I f no processing occurs on site, the upstream sector includes the first transportation links to the refinery.

Upstream industry

Produces petroleum, also referred to as upstream sector; namely, exploration and development companies, seismic ,and drilling contractors, service rig operators, engineering firms.


United Kingdom Continental Shelf.

USGS Assessed Petroleum Volumes

The quantities of oil, gas, and natural gas liquids that have the potential to be added to reserves within some future time frame, which for this assessment is 30 years. The USGS assessed petroleum volumes include those from undiscovered accumulations, whose sizes are greater than or equal to the selected minimum accumulation size, and from the reserve growth of fields already discovered.



The resistance to flow or “stickiness” of a fluid.


The control equipment fitted to the top of the well consisting of outlets, valves, blowout preventers, etc.

Wet Gas
Natural gas containing condensable hydrocarbons.

A well drilled in an unexplored area.

Working capital
Current assets minus current liabilities, shows a company’s ability to meet its short-term obligations.

Working Interest
an interest in an oil and gas lease that gives the owner of the interest the right to drill for and produce oil and gas on the leased acreage and requires the owner to pay a share of the costs of drilling and production operations. The share of production to which a working interest owner is entitled will always be smaller than the share of costs that the working interest owner is required to bear, with the balance of the production accruing to the owners of royalties. For example, the owner of a 100% working interest in a lease burdened by a landowner’s royalty of 12.5% would be required to pay 100% of the costs of a well but would be entitled to retain 87.5% of the production.

Major repairs or modifications which restore or enhance production from a well.


The injection of water into an oil reservoir to ‘push’ additional oil out of the reservoir rock and into the wellbores of producing wells.

Well DataStore

Run by CDA, one of the largest shared online stores of digital well report and log data in the world.

Well log

A record of geological formation penetrated during drilling, including technical details of the operation.


West Texas Intermediate, a type of crude oil commonly used as a price benchmark.