2-D Seismic Seismic data is used to map subsurface formations. A 2-D survey reveals a cross section of the subsurface.
3-D Seismic An 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.
Annular space The space between a well’s casing and the wall of the borehole.
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.
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.
BBL One Barrel, or 42 U.S. Gallons
BCF The cubic foot is a standard unit of measure for gas at atmospheric pressure.
BCFE Billions of Cubic Feet Equivalent
BCFG Billion Cubic Feet Gas
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.
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.
BOP An assembly of heavy-duty valves attached to the top of a well casing to control pressure. (blowout preventer)
BOPD Barrels of Oil per Day
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.
Brine Water Water is that is heavily saturated with salt used in various well completion and workover activities.
(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.
BWPD   Barrels of Water Per Day


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.
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.
Carry to Casing Point A participant (carried party) in drilling, such as a promoter or prospect generator, who is free of drilling and completion costs on a well up to a point.  The costs are borne by the other participants (carrying parties) such as investors and/or working interest owners.
Carry to the Tanks A participant (carried party) in drilling, such as a promoter or prospect generator, who is free of drilling and completion costs on a well up to a point.  The costs are borne by the other participants (carrying parties) such as investors and/or working interest owners.
Cased-Hole A wellbore lined with a string of casing or liner to protect the open hole from fluids, pressures, wellbore stability problems or a combination of these. Although the term can apply to any hole section, it is often used to describe techniques and practices applied after a casing or liner has been set across the reservoir zone, such as cased-hole logging or cased-hole testing.
Casing Steel pipe placed in an oil or gas well as drilling progresses to prevent the wall of the hole from cave-in, to prevent seepage of fluids, and to provide a means of extracting petroleum if the well is productive.
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.
Cavings Rock Fragments 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 drill pipe 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.
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.
Compression To move natural gas through pipelines, it must be compressed to save space and push it further down the pipeline.  Most gas is compressed at 1,000 psi (pounds per square inch).
Condensate Liquid hydrocarbons separated from natural gas, usually by cooling.
Confirmation well A well drilled to “prove” the formation encountered by an exploratory well.
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.
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.


Deductions Tax items which may be subtracted from gross income to arrive at taxable income in Federal income tax computations.
Delay rental Cash payments to the mineral rights owner (lessor) by the working interest owner (lessee), for the privilege of postponing the commencement of drilling operations on the leased property.
Delineation well Or appraisal well is drilled near a discovery well. It helps define the boundaries of the oil or gas reservoir, and assists in deciding whether to incur additional spending to drill more wells to fully develop the field and produce the oil or gas. A delineation or appraisal well can be deemed a dry hole.
Deliverability A well’s tested ability to produce.
Depletion The method of computing a tax deduction against revenue from a producing well to account for a reduction in value of extractable natural resources.  For most individual investors this deduction is 15% of gross income (percentage depletion allowance).
Development Well A well drilled in a field where oil or gas is already producing. A development well is rarely a dry hole
Dewatering The process of removing water from a hydrocarbon-containing formation that then stimulates the removal of oil and/or natural gas from that formation.
Diesel oil A petroleum fraction composed primarily of aliphatic (linear of unbranched) hydrocarbons. Diesel oil is slightly heavier than kerosene.
Directional drilling Drilling at an angle, instead of on the perpendicular, by using a whipstock to bend the pipe until it is going in the desired direction. Directional drilling is used to develop offshore leases, where it is very costly and sometimes impossible to prepare separate sites for every well; to reach oil beneath a building or some other location which cannot be drilled directly; or to control damage or as a last resort when a well has cratered. It is much more expensive than conventional drilling procedures.
Division Order A contract for the sale of oil or gas, by the holder of a revenue interest in a well or property, to the purchaser (often a pipeline transmission company).
Domestic production Oil and gas produced in the United States as opposed to imported product.
Downdip A description of a relative position in a non-horizontal formation.  In non-horizontal formations the rock strata (reservoir rock) lays at some angle different than “flat.”  This angle allows for a separation of gas from oil and from water by simply density with the gas being at the top of the strata.  Downdip of the gas would be the water/gas contact zone or oil/gas contact zone.
Downhole Refers to equipment or operations that take place down inside a borehole.
Downstream All operations taking place after crude oil is produced, such as transportation, refining, and marketing.
Drill bit The part of the drilling tool that cuts through rock strata.
Drill string Also called drill pipe or drill stem. Thirty-foot lengths of steel tubing screwed together to form a pipe connecting the drill bit to the drilling rig. The sting is rotated to drill the hole and also serves as a conduit for drilling mud.
Drilling The act of boring a hole through which oil or gas may be produced if encountered in commercial quantities.
Drilling mud A mixture of clay, water, chemical additives, and weighting materials that flushes rock cuttings from a well, lubricates and cools the drill bit, maintains the required pressure at the bottom of the well, prevents the wall of the borehole from crumbing or collapsing, and prevents other fluids from entering the well bore.
Drilling platform An offshore structure with legs anchored to the sea bottom that supports the drilling of up to 35 wells from one location.
Drilling Rig The surface equipment used to drill for oil or gas, consisting chiefly of a derrick, a winch for lifting and lowering drill pipe, a rotary table to turn the drill pipe, and engines to drive the winch and rotary table.
Drillstem test A test through the drill pipe prior to completion to determine if oil or gas is present in a formation.
Dry hole Occurs when no oil or gas is found in the well, or the quantity of oil or gas that was found is insufficient to justify the expense of bringing the well into production.
Dry natural gas Is fairly pure methane gas. It is natural gas that remains after (1) the liquefiable hy­drocarbon portion has been removed from the gas stream (i.e., gas after lease, field, and/or plant separation); and (2) any volumes of non-hydrocarbon gases have been removed where they occur in sufficient quantity to render the gas unmarketable. Note: Dry natural gas is also known as consumer­grade natural gas.
Dual completion Completing a well that draws from two or more separate producing formations at different depths. This is done by inserting multiple strings of tubing into the well casing and inserting packers to seal off all formations except the one to be produced by a particular string.