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. See also development well.
Block: Subdivision of sea area for the purpose of licensing to a company or companies for exploration/production rights. A UK block is 1/30 of a quadrant and is approximately 200 - 250 sq. km (a quadrant is one degree by one degree).
Barrel: (bbl: barrel; mmbbls: million barrels) A unit of measure for oil and petroleum products equal to 42 US gallons or 35 imperial gallons. Blow-out:Accidental escape of oil or gas from a well during the drilling stage. Blow-out Preventer (BOP): High pressure valve fitted to the top of the casing to prevent blow-outs.

Compressor: An engine used to increase the pressure of natural gas so that it will flow more quickly through a pipeline. Condensate: Liquid hydrocarbons separated and recovered from a condensate gas reservoir. Decommissioning/Abandonment: Removal of production equipment and facilities from depleted oil fields.
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. Directional Drilling: Also known as deviated drilling; technique used in production drilling whereby wells are drilled at an angle from a central point so that a number of development wells can be drilled from a single drilling facility. Downhole: A term used to describe tools, equipment, and instruments used in the wellbore, or conditions or techniques applying to the wellbore. Downstream: Refining of crude oil and the marketing and distribution of oil products that occur after refining, as opposed to upstream.

Downtime: The time during which offshore operations cannot be continued owing to adverse weather conditions, mechanical problems, or other factors. Drill-bit: The cutting head attached to the drill-pipe.
Drilling Muds or Fluid: Fluid, containing barytes, which is pumped through the drill-string to the bottom of the well, whence it rises to the surface through the space between drill-string and bore-hole wall. It acts as a lubricant and is used to control flow. Dry hole: Any exploratory or development well that does not find commercial quantities of hydrocarbons. E&P: Exploration and production. The "upstream" sector of the oil and gas industry. Equity: Share or interest in an oil or gas license or field. Exploratory well: A hole drilled: a) to find oil or gas in an area previously considered unproductive; b) to find a new reservoir in a known field, i.e., one previously producing oil and gas from another reservoir, or c) to extend the limit of a known oil or gas reservoir.

Farm in: Where a company to joins a joint venture in return for paying disproportionately for future joint venture operations. Field: An area consisting of a single reservoir or multiple reservoirs all grouped on, or related to, the same individual geological structural feature or stratigraphic condition. The field name refers to the surface area, although it may refer to both the surface and the underground productive formations. Floater: An offshore drilling platform without a fixed base, usually held in position by anchor chains.
FPSO: Floating Production Storage and Offloading. Integrated: When applied to an oil company, it indicates a firm that operates in both the upstream and downstream sectors (from exploration through to refining and marketing). Jacket: Supporting structure for an offshore platform. Jack-up: Mobile offshore drilling platform with retractable legs, on which the platform rests on the seabed when operational. Joint venture: Oil companies generally participate in oil and gas projects through their equity share in a joint venture, usually unincorporated. The relationship between the companies is governed by a joint venture agreement. Lease: 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 may be located.

License: An exploration license permits only geological and geophysical surveying and the drilling of shallow wells; a production license confers exclusive rights on the licensee to search and bore for and get petroleum. Log: The results of a survey which gathers information about the subsurface formations. Logs typically consist of several curves on a long grid that describe properties within the wellbore or surrounding formations that can be interpreted toprovide information about the location of oil, gas, and water. Also called well logs.

mmcf: million cubic feet. mmcfd: million cubic feet per day. mmscfd: million standard cubic feet per day. bcf: billion cubic feet. Midstream: 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. OPEC: Organisationn of Petroleum Exporting Countries, founded in 1960. Current members are Algeria, Indonesia, Iran, Iraq, Kuwait, Libya, Nigeria, Qatar, Saudi Arabia, UAE, and Venezuela. Operator: One member of a joint venture is appointed operator and has the responsibility of carrying out operations on behalf of the joint venture.
P&A (plugged and abandoned): A depleted well or dry hole that has been (typically) filled with cement with all surface equipment removed. Plateau Level: The level of peak production reached by an oil or gas field.
Platform: A fixed structure resting on the seabed or piled into it from which development wells are drilled, using directional drilling, to exploit an oil or gas field. To date, these platforms are of two kinds, although several novel designs are in existence. Gravity structures, either concrete or hybrid with concrete base and steel legs and superstructure, which rest on the seabed by virtue of their own weight, or steel, which are piled into the seabed. Reservoir: A subsurface, porous, permeable rock formation in which oil and gas are found. Seismic: Data that is acquired by reflecting sound from underground strata and is processed to yield a picture of the sub-surface geology of an area. Semi-submersible: Mobile offshore drilling platform with floats or pontoons submerged to give stability while operating, kept in position by anchors or dynamic positioning. Spud, to: To commence drilling operations. Topsides: The top part of a platform positioned on the jacket. UKCS: United Kingdom Continental Shelf. Upstream: Upstream covers the exploration, production and transport prior to refining. Wellhead: The equipment at the surface of a well used to control the pressure and flow of fluids; the point at which the hydrocarbons and water exit the ground or sea bed.