Anticline: A tectonic structure in which strata are folded so as to form an arch or dome.
Anticlinal trap:A hydrocarbon trap formed by the upward bowing of strata into a dome or arch.
API:American Petroleum Institute.
Appraisal well: A well drilled to determine the extent of hydrocarbons discovered inprevious well on the same structure.
Barrel (bbl): The unit of volume measurement used for petroleum and its products.
1 barrel = 42 U.S. Gallons = 35 Imperial Gallons (approx.) or 159 litres (approx.)
BCF or bcf: Billion cubic feet (109 cubic feet) = 28.317 million cubic metres.
BOPD or bopd: Barrels of oil per day.
Basin: A depression of large size in which sediments have accumulated.
Carbonates: Sedimentary rocks composed of calcium and/or magnesium carbonate e.g. limestone, chalk.
Claystone: A sedimentary rock composed predominantly of particles less than silt size usually comprising clay minerals.
Closure: The area within the lowest closing contour of a structure, also, a closed structure. See four-way dip closure.
Condensate:Hydrocarbons (predominantly pentane and heavier compounds) which spontaneously separate out from natural gas at the wellhead and condense to liquid.
Depocentre: An area or site of maximum deposition in a sedimentary basin.
Depression: A low place of any size on the Earth's surface, also may refer to a sedimentary trough or basin.
Deposition: The laying down of potential rock forming material i.e. sediments.
Devonian: A geological time period approximately 410 to 354 million years ago.
Dip: The angle of the plane of a bed relative to the horizontal.
Dry hole: A well drilled without finding gas or oil in commercial quantities.
Eocene: A geological time period approximately 55 to 34 million years ago
Exploration well: A well drilled to determine whether hydrocarbons are present in a particular area or structure.
Facies/Lithofacies: The rock record of any sedimentary environment, including both physical and organic characters.
Fault: A fracture in the Earth's crust along which the rocks on one side are displaced relative to those on the other.
Fault trap: A hydrocarbon trap which relies on the termination of a reservoir against a seal due to fault displacement.
Field: A geographical area under which an oil or gas reservoir lies.
Fold/Folding:A bend in strata, commonly a product of deformation.
Formation: A unit in stratigraphy defining a succession of rocks of the same type.
Four-way dip: A structural feature seen on orthogonal seismic lines to dip away in all four possible directions, closure indicating that any hydrocarbons beneath a sealing stratum will be trapped in this feature.
Gas in Place (GIP): An estimated measure of the total amount of gas contained in a reservoir and, as such, a higher figure than Recoverable Gas.
Geology: The science relating to the history and development of the Earth's crust.
Geophysics: The physics of the Earth; a hybrid discipline involving a combination of physical and geological principles.
Hydrocarbons: Naturally occurring organic compounds containing only the elements hydrogen and carbon that may exist as solids, liquids or gases.
Horizon: A term used in seismic interpretation to identify the signal reflected from a particular layer of rock.
Intraformational: Existing within a geological formation, for example a single shale bed in an alternating sequence of sands and shales may be an intraformational seal.
Lacustrine: Sediments deposited in a lake environment.
Lead: Inferred geologic feature or structural pattern requiring investigation.
Licence: An authority to explore for or produce oil or gas in a particular area issued to a company by the governing state.
Limestone: A rock composed of calcium carbonate.
Lithology: The physical and mineralogical characteristics of a rock.
Marine: Deposited in the sea.
Mature (source): The condition, caused by pressure, temperature and time, in which organic matter in a potential source rock will be converted to hydrocarbons.
Migration: The movement of hydrocarbons from regions of higher to lower pressure.
MMSTB or mmstb:Millions of standard barrels.
MMCFD or mmcfd: Millions of cubic feet per day = 28,317 cubic metres per day.
Net Pay: The subsurface geological layer where a deposit of oil or gas is found in potentially commercial quantities.
Oil: A mixture of liquid hydrocarbons of different molecular weights.
Oil Field: A geographical area under which an oil reservoir lies.
Oil in Place (OIP) also Oil Initially in Place (OIIP): An estimated measure of the total amount of oil contained in a reservoir and, as such, a higher figure than Recoverable Oil.
Paleocene: A geological time period approximately 65 to 55 million years ago.
Permeability: A measure of the capacity of rock or stratum to allow water or other fluids such as oil to pass through it.
Petroleum: A generic name for hydrocarbons, including crude oil, natural gas liquids, natural gas and their products.
Petroleum system: The set geological conditions which give rise to petroleum accumulations.
Petrophysical: The physical properties of rocks, in this context, as measured by well logs.
Pipeline: A pipe through which oil, its products, or gas is pumped between two points, either offshore or onshore.
Porosity: The ratio of the volume of pore space in rock to its total volume, expressed as a percentage.
Prospect:A feature sufficiently defined to warrant the drilling of a well without the necessity of further investigation.
Quartz: A mineral composed of silicon dioxide.
Recoverable Gas: An estimated measure of the total amount of gas which could be brought to the surface from a given reservoir; this is usually of order 60% - 70% of the estimated Gas in Place.
Recoverable Oil: An estimated measure of the total amount of oil which could be brought to the surface from a given reservoir; this is usually less than 50% of the estimated Oil in Place and commonly in the 20% to 40% range.
Reservoir: Pervious and porous rocks (usually sandstone, limestone or dolomite) capable of containing significant quantities of hydrocarbons.
Risk: An expression of uncertainty (high risk) or uncertainty (no risk) often relating to the presence of principal geological factors controlling oil accumulations.
Sandstone: A sedimentary rock composed predominantly of sand sized grains, usually quartz.
Seal:An impermeable rock (usually claystone or shale) that prevents the passage of hydrocarbons.
Seismic survey: A technique for determining the detailed structure of the rocks underlying a particular area by passing acoustic shock waves into the strata and detecting and measuring the reflected signals.
Sediment: Solid material, whether mineral or organic, which has been moved from its position of origin and redeposited.
Sedimentary rock: A rock formed as a result of the consolidation of sediments.
Shale: A claystone exhibiting a finely laminated structure.
Show: An indication of oil or gas from an exploratory well.
Silt/Siltstone: Rock intermediate in texture and grain size between sandstone and claystone.
Source rocks: Rocks (usually claystone or coal) that have generated or are in the process of generating significant quantities of hydrocarbons.
Stratigraphy: The study of stratified rocks, especially their age, correlation and character.
Structural Trap:A trap formed as a result of folding, faulting or a combination of both.
Structure: Deformed sedimentary rocks, where the resultant bed configuration is such as to form a trap for migrating hydrocarbons.
Structure Map: A contour map on a given horizon using depths generally derived from seismic two way times by assuming an average velocity value.
Tertiary era: An era of geological time approximately 65 to 1.8 million years ago.
Time Structure Map: A contour map on a given horizon derived from seismic two way times.
Trap:A body of reservoir rock, vertically or laterally sealed, the attitude of which allows it to retain the hydrocarbons that have migrated into it.
Trend: A strike direction of a geological feature.
TWT(Two Way Time):A measure of the time taken for a seismic wave to reach a reflecting horizon and return to a surface geophone. Measured in milliseconds (msec). May be converted to depth by applying an average velocity estimate or calculation.
Unconformity: Lack of parallelism between rock strata in sequential contact, caused by a time break in sedimentation.
Updip:The direction leading most directly to higher elevations on an inclined stratum or structure.
Uplift: Elevation of any extensive part of the Earth's surface relative to some other part.