Glossary of Terms
3D Seismic Data: (see Seismic Data) Seismic data that is recorded, processed and interpreted in a three-dimensional volume instead of individual two-dimensional lines. The most common oil and gas exploration technology currently in use in the United States.
Barrel (bbl): A unit of measurement commonly used in quoting liquid hydrocarbon volumes.
1 barrel = 42 U.S. gallons
35 imperial gallons (approximately)
159 liters (approximately)
Basin: A large-scale depression in the earth's surface containing relatively thick deposits of sedimentary rocks.
Closure: On an isolated structural high, the area enclosed by the lowest closing contour
Conglomerate: A coarse-grained clastic sedimentary rock set in a fine-grained matrix of sand and silt.
Cretaceous: The last period of the Mesozoic Era, roughly 63 to 135 million years ago.
Development Well: A new well to be drilled in an established reservoir
Deposition: The process of depositing unconsolidated sediments, usually in a basin.
Dip: The angle that a rock surface or rock formation forms with respect to the horizontal. Can be referenced as degrees or feet per mile, in the case of depth, or, in the case of seismic reflection data, in time (e.g. milliseconds per km).
Dry Hole: A well in which no commercial hydrocarbons were discovered.
Electrical Well Log: A device which records rock physical properties in well bores.
Eocene: The Epoch of Cenozoic time from 34 to 55 million years ago.
Fault: Any brittle failure of rock layers along which rocks are displaced on one side relative to the other.
Field: A subsurface accumulation of hydrocarbons.
Formation: A formal term used to reference a genetically related rock unit.
Gas Show: A significant increase in gas detector response from an increasing concentration of natural gas in the mud system of a drilling well.
Geology: The study of the earth and the processes affecting its crust.
Geophysics: The study of rock properties and stratigraphy through the use of analytical methods involving various types of data collection and interpretation, often seismic.
Hydrocarbons: A compound of the elements hydrogen and carbon, in either liquid or gaseous form. Natural gas and petroleum are mixtures of hydrocarbons.
Horizon: A term describing a layer of rock, most typically associated with a seismic reflection.
Isochron: A line on a map that connects points of equal thickness (in time) of a geological horizon.
Isopach: A line on a map that connects points of equal thickness (in feet or meters) of a geological horizon.
Limestone: A sedimentary rock composed primarily of calcium carbonate.
Lithology: The physical, sedimentary, or mineralogical characteristics of a rock.
MCF: 1,000 standard cubic feet of natural gas as measured at 14.65 psi and 60 degrees Fahrenheit.
Millidarcy (md): A unit of measurement used to describe permeability, i.e., the tendency for liquids to flow through a rock unit. High permeability is a positive reservoir characteristic.
Miocene: The Epoch of Cenozoic time from 5 to 24 million years ago.
Natural Gas: (See Hydrocarbons)
Oil Field: A subsurface accumulation of hydrocarbons.
Permeability: A measure of the ability of liquids to flow through a porous solid.
Petroleum: (See Hydrocarbons)
Pipeline: A pipe through which any hydrocarbon or its products is delivered to an end user.
Porosity: The percentage of open pore space in a rock.
Prospect: An undrilled, untested, and unproven, hydrocarbon trap.
Proven Reserves: Estimated quantities of hydrocarbons that geological and engineering data demonstrate will be recoverable from known oil and natural gas reservoirs under existing economic and operating conditions.
Recoverable Reserves: That proportion of the oil and/or natural gas in a reservoir that can be removed using currently available techniques.
Reserves: The volume of oil or natural gas that can be recovered from the subsurface. Generally used in the context of commerciality.
Reservoir: A porous rock unit in which hydrocarbons occur in an oil or gas field.
Risk: A measure of uncertainty relating to the likelihood of finding and producing hydrocarbons, or the likelihood that any or all of the individual geological elements required for the accumulation of hydrocarbons is met. Commonly considered to be the chance of commercial success.
Sandstone: A sedimentary rock composed primarily of sand sized grains, usually quartz.
Seal: An impermeable rock unit that prevents or inhibits hydrocarbons from escaping from the reservoir.
Sediment: Generally, water borne debris that settles out of suspension.
Sedimentary Rock: A layered rock resulting from a consolidation of sediment, e.g. a clastic rock such as a sandstone or a shale.
Seismic Data: A technique that utilizes sound waves to analyze various attributes of subsurface rock layers. The sound waves are projected and recorded from the surface.
Shale: A fine-grained detrital sedimentary rock, formed by the compaction of clay, silt, or mud.
Show: An indication while drilling that hydrocarbons are present in the well.
Silt: A detrital particle finer than fine sand and coarser than clay
Source Rock: An organic rich rock (typically shale or deepwater carbonate) capable of generating hydrocarbons under certain conditions of temperature and pressure.
Stratigraphic Trap: Generally, a hydrocarbon trap that is the result of lithologic changes rather than structural deformation.
Stratigraphy: The study of the vertical and horizontal distribution of stratified rocks, with respect to their age, lateral equivalence, and environment of deposition.
Structural Trap: Generally, a hydrocarbon trap formed by dipping rock layers and/or faults.
Structure: A geological feature usually higher in elevation than the surrounding rock, formed by local deformation of the rock layers.
Tertiary: The first period of the Cenozoic Era, roughly 2 to 65 million years old.
Trap: A structure capable of retaining hydrocarbons.
Trend: A particular direction in which similar geological features are repeated. Commonly used to describe the distribution of producing reservoirs aligned with a series of geological features,
Undeveloped Reserves: Oil and/or natural gas in a reservoir that are expected to be recovered from a new well drilled on acreage that is directly offsetting a producing well.