Glossary

Acid stimulation	Injection of acid into a reservoir, to increase the production of hydrocarbons.
API gravity	An arbitrary scale of degrees, named after the American Petroleum Institute, by which a crude oil’s specific gravity (density relative to water) is measured. The larger the API degree, the lighter the oil.
Associated gas	Natural gas associated with oil accumulations by virtue of its being dissolved in the oil under reservoir temperatures and pressures or by virtue of its overlying the oil.
Black oil	Liquid hydrocarbons derived from crude oil. As such, the term excludes condensate, which is derived from natural gas.
Carbonate stringer	Carbonate rock formation encased in salt. Such formations are found in south Oman.
Casing	Joined steel pipes used to line a borehole. The casing is secured to the borehole wall with cement.
Cemented completion	Method of completing well in which tubulars — either casing or production tubing — is fixed in place with cement.
Condensate	Light, liquid hydrocarbons that condense out of natural gas upon a change in pressure.
Downhole separation	The segregation of oil from water in a well rather than at the surface.
Drag reducers	Chemical agents added to a liquid to reduce the resistance to its flow through pipelines.
Drop-out	The formation of condensate in a gas reservoir as a result of pressure changes due to production.
Electric submersible pump (ESP)	Electrically driven pump that is installed in oil wells.
Expandable tubulars	Oilfield tubing that can be expanded to a larger diameter by drawing a cone through it.
Fairway	Geographic area in which a particular play is known to yield hydrocarbons.
Finding cost	Total annual exploration expense divided by exploration reserves booked during the year.
Fracture stimulation (fraccing)	Attempt to increase production from a well by subjecting the reservoir to enough hydraulic pressure for it to crack. A granular "proppant" is injected into the cracks to hold them open when the pressure is released.
Frontier exploration	Exploration for hydrocarbons that is focused on previously unexplored formations.
Gas anchor	Device to allow gas dissolved in well liquids to escape before the liquids are pumped to the surface.
Gas injection	Injection of natural gas into an oil reservoir to maintain its pressure, thereby assisting the oil production from the reservoir.
Gas lift	Method of increasing the natural flow of oil from a well by injecting gas into the well fluids, thereby lightening the fluid column.
Geosteering	Adjusting the direction of drilling by means of the rock properties detected at or near the drillbit.
Gravel pack	A type of well completion based on surrounding the production tubing with gravel.
Horizontal well	Well that traverses a formation at an angle 90 degrees from the vertical.
Intelligent pig	Device that detects flaws in a pipeline as it travels down the pipeline.
Logging	Recording the physical properties of the rock around a borehole, as a function of depth. Some of the key properties measured are the rock’s electrical resistivity, its natural radiation and speed of sound through it. Such measurements provide clues as to whether oil or gas is present in the rock and whether it is likely to flow into a well.
Lost-time incident frequency (LTIF)	Measure of safety. The number of recorded incidents in which an employee is rendered incapable of working (per million working hours).
Lost-time occupational illness frequency (LTOIF)	Measure of occupational health. The number of cases of occupational illnesses that have resulted in an employee's incapacity to work (per million working hours).
Multi-lateral well	Well with multiple branches.
Multi-phase pump	Pumps that can move a mixture of crude oil, natural gas, water and perhaps even some solid particulate matter down a pipe.
Near-field exploration	Exploration for hydrocarbons that is focused on in the vicinity of existing oil and gas fields.
Non-associated gas	Gas accumulations that exist independently of any oil accumulations.
Party-month	Measure of seismic exploration activity: one seismic-survey team conducting operations for one month equals one party-month.
Peephole well	A small-diameter pilot hole drilled from the surface to appraise a reservoir.
Play	Particular combinations of subsurface phenomena (reservoir rock, sealing layer, hydrocarbon source and geological structure) that can result in the accumulation of hydrocarbons.
Porosity	Percentage of the bulk volume of a rock taken up by pores, the voids between mineral grains. Hydrocarbons in reservoir rock are contained in such pore spaces.
Pre-stack depth migration (PSDM)	Shifting of seismic traces from their recorded positions to their true positions before the traces are averaged to reduce spurious noise
Pre-stack imaging (PSI)	Brining seismic reflections into focus before the component seismic traces are averaged to reduce spurious noise.
Production (or produced) water	Highly saline water that is commonly found with crude oil in underground reservoirs.
Proppant	Granular material injected into cracks opened up in a reservoir during a fracture-stimulation treatment. The proppant is intended to hold the cracks open, so that oil or gas can flow through them to a well.
Recovery factor	That fraction of the original oil-in-place or gas-in-place that is expected to be ultimately withdrawn from a reservoir. It is generally expressed as a percentage.
Reserves	The estimated quantities of oil and gas that geological and engineering data indicate, with reasonable certainty, to be recoverable in future years from known reservoirs under existing economic and operating conditions.
Reservoir	Hydrocarbon-bearing rock formation. There may be more than one reservoir in a field.
Scope for recovery (SFR)	Classification of hydrocarbon resources when their development options are not yet firm enough to classify them as reserves.
Seismic inversion	Derivation or estimation of rock properties on the basis of seismic data.
Separator	Apparatus that divides the fluid mixture coming out of a well into its oil, gas and water components.
Sidetracks	A well drilled out from an existing well.
Slip-sweep seismic technique	Technique for land-based data acquisition in which the signals emitted and received from different seismic sources (truck-mounted vibrating plates) are allowed to overlap. Because of the overlapping signals, more data can be collected in a given amount of time.
Sour crude	Crude oil containing more than 2.5% sulphur.
Steam injection	Method of enhanced oil recovery involving the injection of steam into a oil reservoir. The heat released by the steam markedly reduces the viscosity of the oil and may cause some of its lighter components to vaporise.
Stock-tank oil initially in place (STOOIP)	Amount of oil originally contained in a rock formation, expressed as barrels at stock-tank conditions (i.e., under atmospheric pressure and room temperature). Only a fraction of the STOOIP is ever produced; the oil that remains is beyond the reach of petroleum engineering in today’s economic climate.
String-month	Measure of rig activity: one rig operating for one year equals 12 string-months.
Supply-chain management	Managing all aspects of supplying goods and services, from the customer's initial order to its final fulfilment.
Three-dimensional seismic survey	A survey involving so many seismic sources and receivers that the underground formations can be imaged in three dimensions rather than as two-dimensional cross-sections.
Tight reservoir	A reservoir with low permeability, i.e., one through which fluids have difficulty flowing.
Total reportable occupational illness frequency (TROIF	Measure of occupational health. The total number of cases of all occupational illnesses (per million working hours).
Underbalanced drilling	Drilling in which the wellbore pressure is deliberately kept below the pressure of the formation being drilled. With this technique, oil can be produced from a well as it is being drilled.
Volume interpretation	Interpretation of seismic data, taking three-dimensions at a time.
Water flooding	Injection of water into a producing formation in order to displace oil toward producing wells.