| 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 in previous 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. |
