Glossary of Terms

Abandonment – permanent dismantling of a production platform or other installation (i.e. plugging of a well).

Anticline – a subsurface geological structure in the form of a gentle arch or an elongated dome. Historically this type of formation has been found favorable to the accumulation of oil and gas. An ideal location to find production is on the crest of the anticline.

API Gravity – a measure of how heavy or how light a petroleum liquid is compared to water. If its API gravity is greater than 10, it is lighter and floats on water; if less than 10, it is heavier and sinks. Most values fall between 10 and 70 API gravity degrees.

Barrel - the traditional unit of measure for oil volume. A barrel is equal to 42 gallons.

Basement Rock – the igneous or metamorphic rock lying below the sedimentary formations in the earth’s crust. Basement rock usually does not contain petroleum deposits.

Basin – a depression in the earth’s crust in which sedimentary materials have accumulated over millions of years.  Basins may contain oil or gas reservoirs.  Much of the production of gas and oil in the United States come from basins, such as the Appalachian Basin, the Permian Basin, the Los Angeles Basin, or the San Joaquin Valley Basin.

Casing – the steel pipes with which a well is lined for protection against collapse of the borehole. The casing also stops unwanted leakage into or from the surrounding rock formation or at the surface.

Casing Point – the point at which the decision is made to complete or abandon the well after reviewing all of the information obtained while drilling the well.

Completion – after a well is drilled and the decision is made to complete it, a number of things must be done. The well must be cleaned out, setting the casing and tubing into the hole, adding surface equipment (pumps, tanks, meters), and perforating the casing so that oil or gas can flow into the well and be brought to the surface. Once a well is completed, it is ready to produce oil or gas.

Commercial Reserves – reserves of oil and gas are restricted to volumes recoverable at an acceptable profitability.

Concession – the deed that entitles the holder to produce from or explore land following the discovery of a commercial reservoir.

Condensate – light hydrocarbon fractions produced with natural gas which condense into liquid at normal temperatures and pressures associated with surface production equipment.

Core Sampling – drilling cylindrical samples of rock in order to study its characteristics.

Cumulative Production – the total amount produced in a certain region/field from inception to present.

Darcy – measurement of rock permeability. The extent to which it will allow a fluid to flow through it. The permeability of most U.S. oil and gas reservoir rocks is measured in millidarcies (thousandths of a Darcy).

Density – ratio of the mass of a given volume of a substance to the mass of an equivalent volume of water.

Dry Hole – an empty or unsuccessful well, sometimes called a “Duster.”

Fault – a structural trap, favorable for the retention of petroleum, formed by the cracking and breaking of a rock plane. It is essential to the creation of a trap that the facing of the rock plane be sealed off by against an impervious formation.

Formation – a rock or mineral deposit or structure covering an area with the same physical properties. The formation will be of homogeneous origin and appearance.

Frac - term used to refer to the method used to increase the deliverability from a producible formation through (fracturing) a well by pumping a liquid or other substance into a well under pressure to crack (fracture) and prop open the created fracture with sand to provide a conduit for the hydrocarbons to easily travel from considerable distances out in the reservoir and into the well bore.

In Place – Description of the total hydrocarbon content of a reservoir, as distinct from reserves, which can be recovered or produced.

Logging – taking measurements of formations, physical conditions, and fluids encountered by a well, together with the records produced by them. The main types of well logs are Electrical, Mechanical, Magnetic, Sonic, and Neutron Density (using atomic material).

Migration – hydrocarbons tend to move up along trends and faults and are often found in formations other than those in which their organic source was deposited. This movement of hydrocarbons, often over considerable distances, is known as migration.

Outcrop – a subsurface rock layer or formation that appears on the surface in certain locations as a result of tilting and erosion.  Part of a strata of rock that comes to the surface.

Perforation - the making of holes in casing and cement (if present) to allow formation fluid to enter the well bore. One common method of perforating is by shooting holes through the casing by means of a special gun lowered into  the hole. Others use shaped charges to penetrate the casing and up to 36” into the surrounding formation.

Permeability – a measure of the resistance offered by rock to the movement of fluids through it. It is measured in darcies or milledarcies.

Plug – to completely seal all or part of a well with cement prior to producing from a higher formation, sidetracking, or leaving the well permanently sealed and abandoned.

Porosity – measures the capacity of the rock to hold oil, gas, or water.  It is   measured in bulk percentage of the volume of rock.

Production – phase of commercial operation of an oil field.

Recovery – the ratio between the volumes of oil or gas produced and producible from a reservoir and the oil or gas originally in place.

Reserves – the estimated amount of oil remaining in the reservoir of an active well less the well’s cumulative production (initial reserves less cumulative production).

Reservoir - a porous or fractured rock formation with a geological seal thus forming a trap for producible hydrocarbons. A common exploration maxim is that a prospective reservoir must possess a related source rock, structure, and seal.

Royalty - the landowner’s or mineral owner’s share of production, free of expenses from production.

Seal – an impermeable stratum or fault of rock beneath or behind which oil and gas cannot flow or accumulate.

Sedimentary Rock – rock formed by the laying down of sediment by seas, streams, or lakes.  Sediment (mineral fragments, animal matter) deposited in bodies of water through geologic ages.  Limestone, sandstone, shale, and salt are examples of sedimentary rock.

Seismic – the transmission of shock waves into the earth then measuring the returned waves recorded by a seismograph. The shock waves are produced by exploding charges of dynamite in shallow holes drilled for this purpose or by trucks that vibrate the ground. Upon striking rock formations, the waves are reflected back to the seismograph. The time lapse is a measure of the depth of the formation.

Source Rocks – the sedimentary layers that contain the organic material that has been transformed into hydrocarbons by heat, pressure, and time.

Syncline – a geologic dipping structure, usually not favorable to the accumulation of oil or gas because of the tendency of the latter to rise in the structure until further escape is blocked.

Solubility – the extent that one material will dissolve in another, generally expressed as mass percent, or as volume percent or parts per 100 parts of solvent by mass or volume. The temperature should be specified.

Tar Sand – another substance from which petroleum can be recovered.  Large deposits are currently mined in Canada. Tar Sand is a synfuel.

Tight Formation – refers to a low permeability and density of a formation usually requiring fracturing to open it.

Tight Sands – low permeability strata that holds hydrocarbons too tightly for conventional extraction processes to bring to the surface at economic rates without special stimulation such as a frac program.

Trap – a special geometrical configuration of rock layers such that oil and gas generated from these source rocks can migrate upward into the reservoir rock but will be unable to migrate further because of an overlying seal.

Tubing – the steel tubular elements in the center of the well by which the effluent is evacuated to the surface. Tubing is normally differentiated from casing by the fact that it is not always permanently installed.

Ultimate Recovery - point in time when production of a well or field comes to an end.

Viscosity – the resistance of a fluid to flow, due to the mutual adherence of its molecules. A measure of a liquid’s resistance to flow. Several viscosity scales are used depending on the type of oil being measured.

Working Interest – the ownership component, which bears all of the costs of drilling, completing, and operating the well.

Zone – the area between two depths in a well containing a reservoir or other characteristics.

Injection Well – a well that is used to inject water or gas back into the formation in order to maintain pressure or to bring a field back under pressure.

Disposal Well – a well drilled into a formation that is safe to receive and store water produced from other wells.