Glossary

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.