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Oil & Gas Glossary


If you don't know much about the oil and gas industry, the sheer amount of jargon to learn can be quite daunting, and those new to the industry or coming in from another Engineering field may struggle with some of the terms used...! That's why we've come up with the Oil & Gas Glossary to help you learn your stuff.

If you think we've missed out anything essential - let us know using the comments at the bottom of this page!


Abandon: Plugging and abandoning a well at the end of its usable life; cleaning up the wellsite and salvaging material and equipment.
Abatement: Methods of reducing pollution.
Acreage: Land leased for exploration or over which the company owns the mineral rig.
Annulus: The space between the borehole wall and casing, between 2 parts of casing, or between casing and tubing.
Appraisal Well: A well drilled to find out the extent and potential production rate of a field.
Aquifier: An underground layer of permeable rock or materials bearing water, from which water can be extracted.
Azimuth: Direction a horizontal well is drilled relative to magnetic North.


Barrel: The measurement used for oil and its products (1 ton = 7.3 barrels).
Bit: The drilling tool which cuts the hole.
Bitumen: Natural flammable substances composed of hydrocarbons and largely free of oxygen.
Block: Sub-division of a quadrant measuring roughly 10 x 20km.
Blow-down: Gas and condensate are produced simultaneously.
Blow-out: When the wellhead valves cannot control the well pressure, causing oil/gas to blow wild at the surface.
Blow-down: Gas and condensate are produced simultaneously.
Borehole: The hole created by the rig (drill bit) in the earth.
BOP: Blow-out preventor, high-pressure valves for safely shutting off uncontrolled flow.
Brine: Mixture of salt water and chemicals, produced after fracturing a well – due to high levels of solids and often metals, it must be treated or disposed of as contaminated waste water.


Casing: A pipe which has been cemented into the well for support and to seal off fluids.
Casing String: Tubing which lines a well after drilling.
Casinghead Gas: Gas produced with oil in oil wells.
Catalytic Cracking: A refining using a catalyst to produce chemical reactions for breaking down large molecules.
CCS: Carbon Capture and Storage, the process which captures CO2 emissions, removes them from the atmosphere and stores them, typically underground.
Cementing: Pumping cement into a wellbore to seal or set a plug for numerous reasons, including abandonment.
Christmas Tree: Valves and fittings on top of the casing to control production rate.
Commercial Field: A field judged to be worth developing due to profitability.
Completion: Installation of wellhead equipment for production.
Compressor Station: Used to increase the gas’ pressure when pumping significant distances through pipelines.
Condensate: Hydrocarbons which are gaseous in the reservoir but become liquid when pressure or temperature is reduced.
Conventional Resources: Accumulations of oil/gas which are easy to permeate and recover.
Coring: Taking rock samples using a core barrel – a tool specialised for this purpose.
Cracker: Cracking petroleum hydrocarbons at high temperature with presence of steam to produce alkenes.
Crane Barge: Derrick Barge, a barge used to lift equipment onto an offshore platform.
Crude Oil: Liquid, unrefined petroleum.
Cuttings: Pieces of rock used by geologists to obtain information.


Derrick: A tower, typically made of open steel framework, which houses most of the drilling controls.
Development Phase: The period in which a field is brought into production by the drilling of wells.
Deviated: Wellbore direction change.
Directional Drilling: Non-vertical drilling.
Distillate Fuel Oils: Fuel oils which are products of distillation.
Downstream: Refining, processing, purification of oil and gas – as well as the marketing and distribution of products derived from oil and gas.
Drilling: Boring holes.
Drilling Rig: A unit for drilling such as a drillship or jack-up unit.
Dry Gas: Gas composed mostly of methane with no or very little heavy hydrocarbons.
Dry Hole: A non-productive well.


Enhanced Recovery: Increased recovery from a pool achieved using outside energy sources.
Environmental Assessment: A study to assess the potential environmental impacts of a project.
EOR: Enhanced Oil Recovery, a process which improves the recovery of oil and gas from a reservoir after the primary production phase.
Equivalent Barrels: The equivalent energy content of one barrel of oil, in natural gas and liquids (roughly 6,000 cubic feet of gas – 6 MCF).
Ethylene: A colourless, flammable gas which is widely used in chemicals.
EUR: Estimated Ultimate Recovery, the amount of reserves remaining on a given date added to the amount already produced.
Exploration Drilling: Drilling to determine the presence of hydrocarbons.
Exploration Phase: The period covering the search for oil / gas through surveys and exploration drilling.
Exploration Well: Wildcat well, a well drilled during the exploration phase.


Field: The area under which a reservoir lies.
Fishing: Retrieving objects from the borehole.
Flaring: The safe burning of natural gas for when there is no way to transport to market or use for other purposes. This is being reduced in response to environmental concerns.
Flowback Water: Water generated during oil and natural gas exploration and development, prior to the well producing.
Formation: A rock layer with distinct characteristics such as rock type.
Formation Pressure: The amount of pressure in the well when the wellhead is shut.
Formation Water: Naturally occurring salt water in the formation.
Fossil Fuel: A fuel source formed from plant or animal remains.
Fracturing: Hydraulic Fracturing, Fracking, pumping high pressure fluid into a formation to boost production rates.
Fracturing Fluid: A mixture of water, sand or proppant and additives used for hydraulic fracturing.
Fugitive Emissions: Emissions (leakages) of gases or vapours from pressurised equipment.


GIS: Geographic Information Systems, computer programs which can store and manipulate information which is referenced geographically.
GHG: Greenhouse gas, gases such as carbon dioxide, methane and nitrous oxide which prevent some energy from leaving the atmosphere, which has the effect of warming the planet’s surface.
Gusher: An oil well at such high pressure that oil flows out of the well head into the air.
GWP: Global Warming Potential, how much heat a greenhouse gas traps in the atmosphere over a time period, shown as a multiple of that for carbon dioxide which is represented by 1.


Heavy Oil: Highly viscous oil which does not easily flow.
Held By Production: The legal process which allows E&P companies to extend the terms of the lease by paying royalties to the rights owner for the life of the well.
Horizontal Drilling: A drilling method where the bit is turned horizontally to produce hydrocarbons located at the same depth.
Hydrocarbon: A compound containing only hydrogen and carbon.
Hydrostatic Pressure: The pressure exerted through fluid weight on a portion of a column of water.


Impoundment: A body of water / sludge confined by a barrier.
Independent: A company involved only in E&P and possibly transportation, but not refining of oil.
Infill Wells: Wells drilled into the same reservoir as each other to limit the distance travelled by oil / natural gas, speeding up recovery.
Injection Well: A well used for pumping water or gas into the reservoir.
Integrated Company: Major oil company; one which is involved in virtually all aspects of the industry from exploration and production through to transportation, refining and marketing.


Jacket: The lower part of an offshore platform.


Land Man: A job role working for an E&P company, negotiating the terms of the lease agreement.
Lay Barge: A barge for laying pipelines.
LCA: Life Cycle Analysis, a methodology used to interpret environmental flows to and from the environment over the process’ life cycle.
LNG: Liquefied Natural Gas, which has been liquefied for transport.
LPG: Liquefied Petroleum Gas, Petroleum held in a liquid state by pressure for storage and handling.


Mechanical Integrity Test: A test to ensure the integrity of the casing.
Methane: The principal constituent of natural gas, methane is both odourless and colourless and absorbs longwave radiation so is considered a greenhouse gas.
Midstream: The movement, measurement and processing of oil and gas from the well.
Mineral Rights: Legal rights allowing for exploration and removal of minerals in a particular location.
Moonpool: A hole in a drillship or semi-sub used for drilling and diving operations.
Mud: Drilling Fluids, base substance plus additives, which is used both for counteracting pressure and lubricating the drill bit.


Natural Gas: Naturally occurring gas which is found alongside crude oil.
Natural Gas Liquids: Hydrocarbons found in natural gas which can be isolated as LPG and natural gasoline.
Net Acres: The amount of the lease owned by a company.


Oil: A mixture of liquid hydrocarbons of different molecular weights.
Oil in Place: Estimation of the amount of oil in reservoir (both recoverable and non-recoverable).
Oil Pool: An underground reservoir or trap containing oil.
Operator: The company drilling wells and producing oil.


Payzone: Rock in which oil and gas are found.
Permeability: The extent to which fluid can flow through the pore and into the well.
Petroleum: Generic name for hydrocarbons.
PIG: Pipeline Inspection Gauge, performs maintenance in a pipeline.
Pipeline: Tubing or piping installed across states, countries and continents to deliver fuel.
Play: An area where prospects with similar characteristics accumulate.United States.
Platform: A permanently affixed offshore structure.
Plugging of Well: Sealing off of fluids to stop fluid from one stratum from escaping into another or from surfacing.
Pooling: Land pooling, the legal process allowing E&P companies to compel land/mineral rights holders to lease or sell their land and/or mineral rights for exploration, drilling, or pipeline installation if enough surrounding neighbours have already agreed.
Porosity: The percentage of void to solids in a porous rock.
Possible Reserves: Reserves with less than 50% chance of being producible.
Primary Recovery: Oil produced using the reservoir’s natural pressure.
Probable Reserves: Reserves with more than a 50% chance of being producible.
Processing Plant: A plant which processes natural gas into propanes, butanes and other products.
Produced Water: Overboard water, water or brine produced from oil and gas wells.
Production Well: A well capable of producing enough oil and gas to justify commercial exploitation.
Propane: A colourless, flammable gas in petroleum and natural gas.
Proppant: Sand or man-made particles pumped during hydraulic fracturing treatment to keep fractures open, allowing oil and natural gas to flow.
Proven Field: A field whose reserves have been determined.
Proven Reserves: Reserves which have been proven to be viable, both economically and technically.


Recompletion: Entering an existing wellbore to establish production from a new zone.
Recoverable Reserves: Recovery Factor, the proportion of oil or gas which can be removed using current techniques.
Redrill Footage: A second hole drilled in close proximity to a failed first hole.
Reenter: Return to an abandoned well.
Refinery: The facility where crude oil is processed into more useful products.
Reserves: Estimated remaining quantities of oil and gas anticipated to be producible.
Reservoir: The underground formation of oil and gas, a porous rock holding hydrocarbons.
Resources: Estimations of quantities of oil and gas, recoverable and unrecoverable; discovered and undiscovered.
Rig: The structures and equipment used in drilling a well.
Rig Down: Disassembling field equipment for transport or storage.
Rig Up: Assembling field equipment to get ready for use.
Riser: In drilling, a pipe between a seabed BOP and floating drilling rig. In production, the pipework joining the wellhead to the Christmas tree.
Roughneck: Job role, crew member who works on the derrick floor, typically screwing together sections of drillpipe.
Roustabout: Job role, crew member who loads and unloads equipment and assists with general rig operations.
Royalty Payment: The money paid by E&P companies to the mineral rights owner of a well.


Seal: A rock unit which inhibits the mixing of fluids and gases between adjacent geologic units, either upwards or laterally.
Seal Formation: The confining rock unit within the carbon dioxide storage assessment unit, designed to inhibit the flow of liquids and gases.
Secondary Recovery: Artificially enhancing pressure in the reservoir through injecting gas, water or other substances.
Shale: Fine-grained sedimentary rock formed by the consolidation of clay, mud or silt.
Shale Gas: Natural gas which can be generated and trapped within shale units.
Shale Oil: Liquid petroleum which can be generated and trapped within shale units.
Shut In Well: A well which is capable of producing but is not at the moment.
Shutdown: A maintenance period during which time production ceases.
Sour Gas: Contaminated natural gas with an unpleasant smell.
Source Rock: Rocks containing hydrocarbons.
Spacing: The distance between wells producing from the same reservoir.
Spud-in: Drilling the first part of a new well.
Stripper Production: The last stage of production a well, usually with low rates of production, as little as a barrel per day.
Surface Location: The location of a well.
Surface Reclamation: Restoration of land used for drilling or production; regrading and vegetating the area.
Suspended Well: A well which has been temporarily capped.


Tension Leg Platform: A type of platform especially useful for deep waters, whereby the surface platform is tethered to the ocean floor by flexible steel tendons.
Tight Gas: Natural gas produced from relatively impermeable rock, usually through hydraulic fracturing or other technologies.
Toolpusher: Job role underneath Drilling Superintendent. They are responsible for day-to-day running of the rig and ensuring availability of equipment.
Tophole: Vertical portion of the hole.
Topsides: Superstructure of a platform.
Trap: A geologic feature which holds hydrocarbons or injected carbon dioxide, caused by the breaking of a rock plane.


Ultrasonic Meter: Ultrasound used to measure flow rates from outside the pipe.
Unconventional Reservoirs: Reservoirs with such low permeability that horizontal hydraulic fracturing other advanced techniques must be utilised for the well to be commercially viable.
Undiscovered: Resources which exist outside of known fields or in undiscovered pools.
Upstream: Oil and gas exploration and production.


Well: The hole drilled in the earth for the purpose of finding and/or producing oil and/or gas.
Wellhead: The structure at the surface of the well which provides the interface for the drilling equipment (Christmas Tree).
Wellhead Revenues: The total value of oil and gas at the wellhead (prior to refinement).
Well Log: Record kept of all wells drilled.
Wet Gas: Gas which contains liquids.
Workover: Attemps to increase flow rate, or remedial work to equipment or pipework.

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