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Oil and Gas Glossary

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3-D Seismic - A relatively new exploration technique used in the search for oil and gas underground structures. The basic premise behind seismic is the same as ultra sound technology used in the medical field. Sound from a shot hole is recorded from geophones and interpreted to give a picture of the underlying structures within the earth. 3-D has now become a common practice to redefine and identify known as well as unknown structures. Many times these structures contain traps that hold oil and gas yet to be discovered.

4-D Seismic - The newest advances in seismic technology which now takes into consideration a 4th dimension; which is time. With 4-D seismic geologists are now able to monitor the movement and the mobility of oil as it is extracted in the production process.


Abstract of title - A chronological history of the ownership of a tract of land.

Acidizing a well - Increasing the flow of oil from a well by pumping hydrochloric acid into the well under high pressure. This reopens and enlarges the pores in the oil-bearing limestone formation.

Acre - The most common of land measure in the United States. A square 210 feet on a side (44,100 sq. ft) would be a bit larger than an acre (43,560 sq. ft). There are 640 acres in a square mile.

Acre-foot - In the U.S., the thickness of a pay zone is measured in feet, and the area of the reservoir is measured in acres. An acre-foot is a volume of reservoir rock that is one acre in area and one foot thick.

AFE (Authorization For Expenditure) - An estimate of the costs of drilling and completing a proposed well, which the operator provides to each working interest owner before the well is commenced.

Annular space - The space between a well's casing and the wall of the borehole.

Annulus of a well - The space between the surface casing and the inner, producing well-bore casing.

Anticline - A geological term describing a fold in the earth's surface with strata sloping downward on both sides from a common crest. Anticlines frequently have surface manifestations like hills, knobs, and ridges. At least 80 percent of the world's oil and gas has been found in anticlines.

API - American Petroleum Institute, a petroleum industry association that sets standards for oil field equipment and operations.

API gravity - The gravity (weight per unit of volume) of crude oil expressed in degrees according to an American Petroleum Institute recommended system. The higher the API gravity, the higher the crude. High-gravity crudes are generally considered more valuable.

Aquifer - An underground water reservoir contained between layers of rock, sand or gravel.

Arab oil embargo of 1973-74 - During the Arab-Israeli conflict in October 1973, Arab oil producers cut off shipments to the Unites States and the Netherlands in retaliation for their support of Israel. At the same time, they cut down production. The shortage was felt by all oil-importing nations, with world prices moving sharply higher. Price and allocation controls suppressed some of this increase in the United States, but gasoline lines were still prevalent.

Asphalt - A solid hydrocarbon which may be deposited within the reservoir rock, in well equipment, or in surface lines and tanks.

Associate gas - The gas that occurs with oil either as free gas or in solution. When occurring alone, it is referred to as unassociated gas.


Back-in - A type of interest in a well or property that becomes effective at a specified time in the future, or on the occurrence of a specified future event.

Barrel Standard - Unit of measurement in the petroleum industry. One barrel of oil equals 42 U.S. gallons.

Basement rock - Igneous or metamorphic rock lying below sedimentary formations in the earth's crust. Basement rock does not contain petroleum deposits.

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

BCF (billion cubic feet) - The cubic foot is a standard unit of measure for gas at atmospheric pressure.

Behind pipe - 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, reserves in the shallower pay zones up the hole are behind the casing.

Biomass - Any organic material, such as wood, plants, and organic wastes, that can be turned into fuel.

Bleeding core - A core sample of rock so highly permeable and saturated that oil drips from it.

Blind pool - Refers to an oil and gas limited partnership which has not committed to specific prospects, leases, or properties at the time of capital formation.

Blowout - A sudden escape of oil or gas from a well, caused by uncontrolled high pressure. It usually occurs during drilling.

Blowout insurance - An insurance policy that protects the insured party (working interest owner) from liabilities which might arise from a blowout during the drilling, completion, or production of a well.

Blue Sky Law - State regulations governing an offering to sell securities within the state.

Bonus Money - paid to a landowner or other holder of mineral rights by the lessee for the execution of an oil and gas lease in addition to any rental or royalty obligations specified in the lease.

BOP (blowout preventer) - An assembly of heavy-duty valves attached to the top of a well casing to control pressure.

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

Bottom-hole pump - A compact, high-volume pump located in the bottom of a well, not operated by sucker rods or a surface power unit.

Bridle - The cable link between the "horsehead" and the pump rod on a pumping unit.

BS&W - (basic sediment and water) Material pumped up with oil and gas which must be separated out.

Btu (British thermal unit) - A standard measure of heat content in a fuel. One Btu equals the amount of energy required to raise the temperature of one pound of water one degree Fahrenheit at or near 39.2 degrees Fahrenheit.

Butane - A hydrocarbon associated with petroleum. It is gaseous at ordinary atmospheric conditions.


Cable drilling - A method of well-drilling that employs a reciprocating, rather than a rotary, motion to penetrate rock. In the nineteenth century, until Drake's time, power was supplied by men. Drake used a steam-powered cable rig. Today, cable rigs are powered by gasoline or diesel engines.

CAOF (calculated absolute open flow) - A figure representing a gas well's theoretical producing capability per day.

Capital Funds - Monies invested in a business for use in conducting the operations of the business.

Capital asset - An asset acquired as an investment, for the purpose of creating a product or service intended to be used in the activities or operations of a business.

Capital costs (Oil & Gas Tax Usage) - For Federal income tax purposes, the costs of capital expenditures which may be recovered by deduction against income (through depreciation and depletion).

Capital expenditure - An expenditure intended to benefit the future activities of a business, usually by adding to the assets of a business, or by improving an existing asset.

Capitalize - To treat certain expenditures as capital expenditures for Federal income tax computations.

Carried Interest - A fractional working interest in an oil and gas lease that comes about through an arrangement between co-owners of a working interest.

Casing Pipe - used in oil wells to reinforce the borehole. Sometimes several casings are used, one inside the other. The outer casing, called the "surface pipe,' shuts out water and serves as a foundation for subsequent drilling.

Casinghead - The portion of the casing that protrudes above the surface and to which control valves and flow pipes are attached.

Casinghead gas - Natural gas produced from an oil well, as opposed to gas produced from a gas well.

Casinghead gasoline - Highly volatile, water-white liquid hydrocarbons separated from casinghead gas.

Cavings Rock - Fagments that break off from the walls of a borehole and fall into the borehole during drilling operations.

Cement - Fluid cement is mixed at the surface, pumped to the bottom of a cased well, forced to flow around the lower end of the casing and up into the space between the casing and the borehole. When the cement solidifies (sets), it holds the casing in place, and provides support.

Cement squeeze - Forcing cement into the perforations, large cracks, and fissures in the wall of a borehole to seal them off.

Choke - An orifice installed in a pipeline at the well surface to control the rate of flow.

Christmas tree - An assembly of valves, gauges, and chokes mounted on a well casinghead to control production and the flow of oil to the pipelines.

Circulate - To pump drilling fluid into the borehole through the drillpipe and back up the annulus.

Clean oil - Crude oil containing less than 1 percent sediment and water; "pipeline oil", oil clean enough to send through a pipeline.

CO2 injection - A secondary recovery technique in which carbon dioxide (CO2) is injected into wells as part of a miscible recovery program.

Coal gasification - The chemical conversion of coal to synthetic gaseous fuel.

Coal liquefaction - The chemical conversion of coal to synthetic liquid fuel.

Cogeneration - The combined production of electrical or mechanical energy and usable heat energy.

Commissions - Payments to qualified agents of the sponsor of a limited partnership, for selling interests in it to investors. Commissions may take the form of a percent of partnership interests sold, an oil and gas interest, or stock in the sponsor's company.

Common carrier - A person or company in the business of transporting the public or goods for a fee. In the industry, a person or company engaged in the movement of petroleum products, like a public utility.

Completed well - A well made ready to produce oil or natural gas. Completion involves cleaning out the well, running steel casing and tubing into the hole, adding permanent surface control equipment, and perforating the casing so oil or gas can flow into the well and be brought to the surface.

Condensate - Liquid hydrocarbons separated from natural gas, usually by cooling.

Confirmation well - A well drilled to "prove" the formation encountered by an exploratory well.

Connate water - The water present in a petroleum reservoir in the same zone occupied by oil and gas considered by some to be the residue of the primal sea, connate water occurs as a film of water around each grain of sand in granular reservoir rock and is held in place by capillary attraction.

Conventional energy sources - Oil, gas, coal, and sometimes nuclear energy, in contrast to alternative energy sources such a solar, hydroelectric and geothermal power, synfuels, and biomass.

Conveyance - Legal term for transferring the title of a property from one party to another, typically by deed.

Core - Samples of subsurface rocks taken as a well is being drilled. The core allows geologists to examine the strata in proper sequence and thickness.

Cracking - The process of breaking down the larger, heavier and more complex hydrocarbon molecules into simpler and lighter molecules, thus increasing the gasoline yield from crude oil. Cracking is done by application of heat and pressure, and in modern time the use of a catalytic agent.

Crude oil - Liquid petroleum as it comes out of the ground. Crude oils range from very light (high in gasoline) to very heavy (high in residual oils). Sour crude is high in sulfur content. Sweet crude is low in sulfur and therefore often more valuable.

Crude oil equivalent - A measure of energy content that converts units of different kinds of energy into the energy equivalent of barrels of oil.

Cuttings - Chips and small rock fragments brought to the surface by the flow of drilling mud as it is circulated and examined by geologists for oil content.


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