Glossary

Platform

An installation used during the production of oil or gas, and for exploration. Oil operations at sea are conducted from both floating platforms and platforms fixed to the seabed.

Accumulation
One or more occurrences of oil or gas confirmed by tests, samples or logging.

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. Such anomalies can also result from other things.

Amplitude
The difference between the maximum displacement of a wave and the point of no displacement, or the null point. The common symbol for amplitude is a.

API gravity
A specific gravity scale developed by the American Petroleum Institute (API) for measuring the relative density of various petroleum liquids, expressed in degrees. API gravity is gradated in degrees on a hydrometer instrument and was designed so that most values would fall between 10° and 70° API gravity. The higher the API gravity the better it is.

Appraisal well
A well drilled to determine the extent and scope of a petroleum find.

Associated gas
Natural gas produced together with oil.

Barrel
Oil production is often given in numbers of barrels per day. One barrel of oil = 159 litres, 0.159 cubic metres. In English the abbreviations bll (barrel) or stb (stock tank barrel) are often used.

Barrels of oil equivalents
Unit of volume for petroleum products. Used when oil, gas and NGL are to be summarised. Abbreviated BOE in English. Also see oil equivalents.

bll (barrel)
See barrel.

Block
A country’s exploration and production area is divided into different blocks that indicate the geographic layout. In the Norwegian section of the North Sea, for example, one block is 15 nautical miles wide and 20 nautical miles long, which corresponds to an area of approximately 575 square kilometres.

Blow-out
Uncontrolled release of  oil, gas or water from an oil well.

BOE
Barrels of oil equivalents

BOEPD
Barrels of oil equivalents per day.

BOPD
Barrels of oil per day.

Brent oil
A reference oil for the various types of oil in the North Sea, used as a basis for pricing. West Texas Intermediate (WTI) and Dubai are other reference oils.

Casing
Steel pipe run into the wellbore after drilling, to serve various functions such as isolation of the wellbore from down hole pressures, contaminating or undesirable fluids, etc at the same time as it protect the surface from down hole contaminants. In general, the casing provides control of the down hole environment.

cf
Cubic foot/feet.

Chalk
Chalk is a soft, white, porous sedimentary rock, a form of limestone composed of the mineral calcite.

Cretaceous
A period in geological history from about 65 to 141 million years ago.

Christmas tree
A surface flow control system that, as a part of the wellhead, contains the master valve, the choke, and other flow control and access valves relative to the production system for that particular well. Is also referred to as the production tree.

cm
Cubic metres.

CNG (Compressed natural gas)
International designation for dry gas or natural gas under pressure in a tanker.

Concession round
Distribution of blocks in a country is done in connection with a concession round under the direction of state authorities.

Condensate
A mixture of the heavier elements of natural gas, i.e. pentane, hexane, heptane etc. Is a liquid at atmospheric pressure. Also called natural gasoline or nafta.

Continental shelf
A gradual, rapidly deepening seabed on a continental plate. Generally situated at a depth of 0-500 metres and is concluded in a continental slope. The ocean area between UK, Denmark and Norway is for example a continental shelf.

Contingent resources
Estimated recoverable volumes from known accumulations that have been proved through drilling. Includes resources classfied under leads. Consideration is taken in repect of the likelyhood of making discoveries.

Core
A cylindrical sample of subsurface rock taken during the drilling operation and returned to the surface for analysis in order to obtain properties of down hole rock and fluid systems.

Cost oil
The share of produced oil that is used to cover ongoing operations costs and to recover past exploration, appraisal and development expenditures

Crude oil
The oil produced from a reservoir, after associated gas is removed in separation. Crude oil is a fossil fuel formed by plant and animal matter several million years ago.

Cubic foot
Unit of volume for gas, most often given in billions of cubic feet.

Cubic meter
Unit of volume for gas, most often given in billions of cubic metres.

Derrick
The steel tower where the drill pipe is raised/lowered, mounted/dismounted and held in place during drilling operations.

Drill bit
Sits on the tip of the drill pipe and has rotating teeth that drill through the bedrock.

Drilling mud (drilling fluid)
Fluid used to lubricate and cool the drill bit and prevent the walls of the well from collapsing. Keeps the flow of oil or gas under control and transports the matrix to the surface. The fluid used is a mixture of water or oil, clay and chemicals.

Drill pipe
Steel pipe that links the drill bit and the drilling platform. The drill pipe consists of connected pipe lengths. The pipe rotates and is also the pipeline for the drilling mud during the drilling operation.

Drill string
The drilling equipement suspending into the wellbore, including drill bit, drill collars, drill pipe, kelly, swivel, and any other components within the drillstring, such as stabilizers, shock absorbers, reamers etc.

Dry hole
An exploratory or development well that does not find commercial quantities of hydrocarbons.

Exploration well
A common term for wildcat and appraisal wells drilled when exploring for oil and gas, to gather facts about the petroleum’s quality, the bedrock’s make-up, the reservoir’s extent and location etc. 

Farm out/farm in
The holder of shares in an oil licence may transfer (farm out) shares to another company in exchange for this company taking over some of the work commitments in the licence, such as paying for a drilling or a seismic investigation within a certain period. In return, the company brought in receives a share in any future revenues. If the conditions are met the company may retain the licence shares if not the shares are taken back by the original holder. This is known as ”farm-in” and ”farm-out”.

Fault
A fracture within rock structures where relative motion has occurred across the fracture surface.

FPSO vessel
A vessel used for production, storage, service and offloading at an oil field at sea. The abbreviation FPSO stand for Floating, Production, Storage and Offloading vessel. 

FDPSO vessel
Os an FPSO vessel with drilling capacity. The abbreviation stand for Floating, Drilling, Production, Storage and Offloading. Is used at the Azurite Field in the Republic of Congo. 

Flaring
Controlled burning of gas that must be released for safety reasons at an oil production facility. Used when impossible to utilise the gas. 

Gas field
A field containing natural gas, but only minor amounts of oil. The gas can contain larger or smaller amounts of condensate that is separated as a liquid when the gas is produced (the pressure and temperature drop).

Gas Oil Ratio (GOR)
The number of cubic feet of natural gas produced with each barrel of oil.

GSm3
Giga standard cubic meter. Volume unit for gas. Equals 1 billion cubic metres of gas at an air pressure of 1.01325 bar and 15 °C.

Heavy crude oil
Heavy oil flows slowly through a reservoir and contains heavier constituents, metals or sulphur. It is therefore more difficult to produce than lighter oil and its combustion is more polluting.

Hydrocarbons
The compounds comprised of the basic elements hydrogen (H) and carbon (C). If an occurrence primarily contains light hydrocarbons, they are most often in gas form in the reservoir, and are then called a gas field. If it is primarily heavy hydrocarbons, they are in liquid form in the reservoir, and called an oil field. Under certain conditions both can exist in the reservoir where a gas cap lies above the oil. Oil always contains a certain element of light hydrocarbons that are freed in production, also known as associated gas. Injection well A well where gas or water is injected to give pressure support in a reservoir. By injecting gas or water (or both), the degree of recovery can be increased as the pressure is maintained by the injection, the hydrocarbons are pushed into the production well.

Injection well
A well where gas or water is injected to give pressure support in a reservoir. By injecting gas or water (or both) the degree of recovery can be increased. As the pressure is maintained by the injection, the hydrocarbons are pushed into the production well.

Jacket
The steel structure of an offshore platform.

Jackup rig
A type of installation used when drilling oil wells at sea. It is fixed to the seabed.

Jurassic
A period in geological history from about 141 to 195 million years ago.

Leads
Leads are possible accumulations of hydrocarbons where more geological data needs to be gathered and evaluations need to be performed before they can be called prospects, where drilling is considered to be feasible.

Licence
A permit to search for and produce oil and gas. Oil and natural gas assets are usually owned by the country in which the accumulation is discovered. The oil companies obtain permission from the respective country’s government to explore for and extract oil and natural gas. These permits can be called concessions, permits, production sharing agreements or licenses depending on the country in question. A license usually consists of two parts an exploration permit and a production license.

Light crude oil
Crude oil that has a high API gravity. Light oil does not need as much specialist treatment during refining and the costs are therefore lower. In addition, light oil is less polluting when used. It therefore commands higher prices when sold. Heavy oil flows slowly through a reservoir and contains heavier constituents, metals or sulphur. It is therefore more difficult to produce than lighter oil and its combustion is more polluting.

LNG (Liquefied natural gas)
Liquid dry gas, primarily methane, that has transformed to liquid form upon cooling to minus 163 °C at atmospheric pressure. One ton of  LNG corresponds to approximately 1,400 cubic metres of gas. LNG is transported by special vessels.

Logs
The result of a survey which gather information from the wellbore and surrounding formations which typically consist of traces and curves. These can be interpreted to give information about the presence of oil, gas and water.

Middle Jurassic
The Middle Jurassic is the second epoch of the Jurassic Period. It lasted from 176-161 million years ago, and is visible at certain levels in the bedrock.

Miocene
The Miocene is a geological epoch of the Neogene Period and extends from about 23.03 to 5.332 million years ago, and is visible at certain levels in the bedrock.

Natural gas
A mixture of hydrocarbons in gas form found in the bedrock, usually 60-95 percent methane.

Net Entitlement
The proportion of production, revenue or reserves and resources that accrue to the oil company after deduction for royalties and taxes.

Net pay zone
The section of the gross reservoir that contributes to production.

NGL (Natural gas liquids)
Liquid gas that consists of three different gases ethane, propane and butane, as well as small amounts of heavy hydrocarbons. Is partially liquid at atmospheric pressure. NGL is transported by special vessels.

Observation well
A well that is equipped with pressure sensors and other measurement instruments to collect additional information about a reservoir. Occurrence An accumulation of petroleum in a geological unit. Delimited by rock types, a contact surface between petroleum and water or a combination of these.

Occurrence
An accumulation of petroleum in a geological unit. Delimited by rock types, a contact surface between petroleum and water or a combination of these. 

Offshore
Designation for operations at sea.

Oil saturation
The percentage of the void space within reservoir rock containing hydrocarbon liquid at reservoir conditions (reservoir fluid pressure and reservoir fluid temperature conditions).

Onshore
Designation for operations on land.

Oil equivalents (o.e.)
An volume unit used when oil, gas and NGL are to be summarised. The concept is tied to the amount of energy released upon combustion of different types of petroleum. Because oil equivalents depend on the amount of energy, it is not constant and different conversion factors are used. In “Oil Field Units”, 5,800 cubic feet of gas = 1barrel of oil  equivalents. According to the Norwegian Petroleum Directorate, 1,000 standard cubic metres of gas = 1 standard cubic meter of oil equivalents.

Operator
A company, which on behalf of one or more companies in a partnership, and after approval from the authorities in the country, leads the work on an oil and gas licence or a field.

OSS vessel
Oil Storage Service vessel 

Permeability
The property of a rock which indicates the presence of flow channels within the rock. The greater the permeability, the greater the presence of those flow channels, and the more easily fluid will flow from the rock.

Petroleum
Collective term for hydrocarbons, whether they occur in solid, liquid or gas state(s).

Platform
An installation used during the production of oil or gas, and for exploration. Oil operations at sea are conducted from both floating platforms and platforms fixed to the seabed.

Play (exploration play)
A conceptual model used for analyzing a geographically and stratigraphic delimited area, where a specific set of geological factors must be present for producible volumes to be proven. Such geological factors are a reservoir rock, trap, mature source rock, migration routes, and that the trap was formed before the migration of hydrocarbons ceased.

Porosity
The porosity of a rock is determined by measuring the amount of cavities inside, and determining what percentage of the total volume that consists of cavities.

Pressure test
A pressure test run in a well, where flow is initiated followed by a shut-in period where the time rate of pressure increase is recorded after shut-in. The data are analyzed for determination of various downhole and reservoir properties and characteristics.

Produced water
Is the water pumped up from an oil well together with oil, gas or other hydrocarbons. The water is separated from the hydrocarbons and purified before it is pumped back down into the reservoir or taken care of in another manner.

Production sharing agreement
See Licens.

Production well
A well used to extract petroleum from a reservoir.

Profit oil
The remaining share of oil produced after royalty and cost recovery through the cost oil. The profit oil is shared according to the production sharing agreement and working interests.

Proven reserves, 1P
Extraction assessed as having a probability in excess of 90% of extraction in the current economical climate.

Proven and probable reserves, 1P
Proven and probable reserves with a probability of in excess of 50% of extraction in the current economical climate.

Recovery forecast
A percentage that indicates how much of the proved, existing reserves are possible to produce.

Refinery
A facility where crude oil is converted to refined products such as petrol, motor oil and bitumen.

Reservoir
An accumulation of oil or gas in a porous type of rock with good porosity, such as sandstone or limestone.

Seismic data
Seismic investigations are made to be able to describe geological structures in the bedrock. Sonar signals are transmitted from the ocean surface or the surface of the ground (pings), and the echoes are captured by special measurement instruments. Used to localise occurrences of hydrocarbons.

Riser
A pipe that transports liquid up from the well to the production platform. During drilling operations, it protects the drilling string from surrounding material.

Risked prospective resources
Prospective accumulations of hydrocarbones which have yet to be proven through drilling. Includes resources classified under Leads. Consideration is taken in repect of the likelyhood of making discoveries.

Sidetrack
Drilling from an existing well path towards a new well target.

Sm3
Volume unit for gas. Standard based on the volume at an air pressure of 1.01325 bar and 15 °C.

Source rock
The geological formation in which oil and gas were created and originate.

Spud
To initiate drilling.

Stratigraphy
A branch of geology which studies rock layers and layering (stratification). It is primarily used in the study of sedimentary and layered volcanic rocks.

Sweet crude oil
Crude oil containing low levels of sulfur compounds, especially hydrogen sulfide [H2S] and carbon dioxide. The facilities and equipment to handle sweet crude are significantly simpler than those required for other potentially corrosive types of crude oil.

Terminal
A land-based facility that receives and stores crude oil and products from oil production at sea. The oil is transported to the terminal by tanker or through pipelines.

Ton oil
One ton of oil is equivalent to 7.5 barrels, depending on the oil’s density.

Trap
A trap is a geologic structure or a stratigraphic feature capable of retaining hydrocarbons in a reservoir. It might be a change in rock type with zero permeability, unconformities, folds, faults etc in the bedrock that prevent the hydrocarbons to migrate from the reservoir

Well
A hole drilled down to a reservoir to look for or extract oil or gas.

Wellhead
The equipment (outlets, valves, etc.) that is fastened to the top of a well to prevent blowout.

Wildcat well
The first well drilled when exploring for oil and gas on a new, defined geological structure (a prospect).

Working interest (WI)
The proportion of production, revenue or reserves and resources that accrue to the oil company before royalties and other taxes.