All A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
Term Definition
/Net pay

The net thickness of an oil reservoir which is capable of producing hydrocarbons.


Area of mutual interest


A structure in the subsurface in which rock layers have been folded to produce an arch or dome.

Appraisal well

A well drilled to evaluate the extent of a discovery made by a previous well drilled on the same trap.

Barrel (BBL)

A unit of measurement commonly used in quoting liquid hydrocarbon volumes.

  • 1 barrel _ 42 U.S. gallons
  • 35 imperial gallons (approx)
  • 159 liters (approx)

A depression in the earth's surface containing relatively thick deposits of sedimentary rocks.


Billion cubic feet, or 28.317 cubic meters. A unit commonly used in quoting volumes of natural gas.


Billion cubic feet of gas.

Behind pipe

A productive reservoir which is isolated from the well bore by the casing.


Bottom hole location.


Barrel of oil.


Barrel of oil equivalent. Used when converting oil and gas into an equivalent unit of volume. Typically, a figure of 6000 CFG per BBLO is used.


Barrels of oil per day, a unit commonly used to describe daily rates of liquids production from a flowing well.


British Thermal Unit. A unit index of energy content in gas.


Steel pipe which lines the well bore from surface. The casing isolates subsurface fluids from the well bore and prevents rock material from sloughing off the sides of the well bore.


Cubic feet of gas

Charge risk

A general term for risk that a source rock exists, that it has been is or still is generating hydrocarbons, that a trap was in place before generation , and that a conduit exists between the source rock and the reservoir.


A modifier describing rocks that were deposited by the mechanical action of water, i.e., being carried in suspension and then dropped when the energy in the flow becomes too weak to support the material. Typically, sandstone and shale.


On an isolated structural high, the area enclosed by the lowest closing contour.


A hydrocarbon phase which separates out from natural gas and condenses into liquids when the hydrocarbons are produced.


Late Mesozoic time; roughly 140 to 65 million years ago.


1000 millidarcies (see definition for mD below).


The process of depositing unconsolidated sediments, usually in a basin.


Dry hole cost. The cost of an unsuccessful well.


The angle that a rock surface forms with respect to the horizontal. Can be referenced as degrees, in the case of depth, or, in the case of seismic reflection data, in time (e.g. milliseconds per km ).


A tool used in logging a well which measures the dip of rock surfaces in the borehole of the well.


Dip Moveout . A correction applied to seismic trace processing to account for dip. (See dip above).


California Department of Conservation/Division of Oil, Gas, and Geothermal Resources

Dry hole

A well in which no commercial hydrocarbons were discovered.

Exploration well

A well drilled into a previously undrilled or noncommercial trap to test for the presence of a new hydrocarbon accumulation.


An association of rock types which share a common trait. In the case of sedimentary rocks, usually used with reference to the environment in which the sediments were deposited (for example, deltaic).


Any brittle failure of rock layers along which rocks are displaced on one side relative to the other.

Fault trap

A structural trap where at least one of the components of closure is formed by offset of rock layers across a fault.


Deformation of a rock surface.


A formal term used to reference a genetically related rock unit (e.g. the Monterey Formation).

Four way dip

A simple structure in which rock surfaces dip in all four directions, thus creating structural closure. Often forms a hydrocarbon trap.


The study of the earth and the processes affecting its crust.


The study of rock properties and stratigraphy through the use of analytical methods involving various types of data collection and interpretation.


Gas in place. The volume of natural gas stored in a subsurface accumulation . Differs from recoverable reserves in that some of this gas will not be recovered to the surface due to properties of the rock and/or gas, and in situ pressure.


Gas-oil ratio: the volume of dissolved gas per barrel of oil.


A term describing a layer of rock, most typically associated with a seismic reflection.


A compound of the elements hydrogen and carbon, in either liquid or gaseous form. Natural gas and petroleum are mixtures of hydrocarbons.


The physical, sedimentary, or mineralogical characteristics of a rock.


Used as a modifier of sedimentary rock to denote deposition in the ocean.


Used in association with source rock. A description applied to organic rich rock which is capable, because of sufficient temperature and burial depth, of generating hydrocarbons.


Millidarcy , a unit of measurement used to describe permeability, i.e., the tendency for liquids to flow through a rock unit. A high permeability indicates a good reservoir.


The movement of hydrocarbons from the source rock to the reservoir.


Million barrels.


Million barrels of oil.


Million British Thermal Units.


Million cubic feet of gas per day. A measure of gas flow rates from a producing well.

Monte Carlo

A methodology for estimating a given quantity based on the statistical distribution of input values on which the quantity depends. Typically, the output quantity is calculated several thousand times (each calculation is called a trial), for each trial using input parameter values extracted randomly according to their statistical distributions. The result is a statistical distribution of output values.


Thousand standard cubic feet at atmospheric conditions.


Net to gross ratio. The percentage of a gross thickness of reservoir with sufficient permeability such that it is capable of flowing hydrocarbons.


Liquid hydrocarbons, generally more viscous and darker in color than condensates.

oil field

A subsurface accumulation of hydrocarbons.

oil window

The depth interval in which source rock can actively generate mobile oil.


Oil in place. The volume of oil held in a reservoir in the subsurface . Not all of this oil can be recovered.


Oil-water contact, which marks the base of an oil accumulation.


In a Monte Carlo simulation, a measure of the high end expectation of a particular parameter's occurrence. For example, a P10 net pay of 150 ft means that there is a 10 per cent. probability that at least 150 ft of net pay will be encountered in a given trial in the simulation.


In a Monte Carlo simulation, the median value of a particular parameter's occurrence. For example, a P50 net pay of 50 ft means that half of the trials in the simulation encountered a value less than 50 ft.


In a Monte Carlo simulation, a measure of the low end expectation of a particular parameter's occurrence. For example, a P90 net pay of 25 ft means that there is a 90 per cent. probability that at least 25 ft of net pay will be encountered in a given trial in the simulation.


A measure of the ability of liquids to flow through a porous solid. (See mD ).


(See Hydrocarbons).


Padre Island National Seashore.


A pipe through which any hydrocarbon or its products is delivered to an end user.


The percentage of open pore space in a rock.


Probability of success (technical, as opposed to commercial).

Potentially Recoverable Hydrocarbons

The volume of hydrocarbons that are estimated to be producible from a given trap. Used in the context of a prospect or an undeveloped hydrocarbon accumulation.


An undrilled or poorly understood, and therefore hypothetical, hydrocarbon trap.


Pre-stack depth migration. A seismic processing technique which utilizes rock velocity models to iteratively arrive at a depth converted seismic data volume.


Pre-stack time migration. A seismic processing technique which approximates PSDM but does not build a depth model. The seismic data volume is in two way travel time.


An event observed on a seismic section that usually corresponds to a buried rock surface.


The volume of oil or gas that can be recovered from the subsurface. Generally used in the context of commerciality.


A porous rock unit in which hydrocarbons occur in an oil field.


A measure of uncertainty relating to the likelihood of finding hydrocarbons, or, the likelihood that any or all of the individual geological elements required for the accumulation of hydrocarbons is met.


A sedimentary rock composed primarily of sand sized grains, usually quartz. A common hydrocarbon reservoir rock.


Standard cubic feet. See MSCF


An impermeable rock unit that prevents hydrocarbons from escaping from the reservoir.


Generally, water borne debris that settles out of suspension.

Sediment rock

A type of rock formed by aggregation of sediments.

Seismic reflection

An event observed on seismic data that corresponds to a given rock layer in the subsurface.

Seismic survey

A tool employing an energy source, such as dynamite, and recording devices used to measure the travel time from a rock layer to the surface. The primary tool used to detect hydrocarbon traps.


A very fine grained rock often thinly layered. An important seal rock.


An indication while drilling that hydrocarbons are present in the well.


A rock whose grain size is intermediate between sand and shale.

Source/source rock

An organic rich rock (typically shale) capable of generating hydrocarbons under certain conditions of temperature and pressure.


Stock tank barrel, the volume of a barrel of oil at the earth's surface as opposed to the corresponding volume in the subsurface.


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.


A geological feature usually higher in elevation than the surrounding rock, formed by local deformation of the rock layers.


Trillion cubic feet of gas.


A period of geological time from approximately 2 to 65 million years ago. Subdivided into the Pliocene, Miocene, Oligocene, Eocene, and Paleocene.

Total depth (TD)

The final depth reached when drilling a well.


A structure capable of retaining hydrocarbons.


A particular direction in which similar geological features are repeated.


True vertical depth. The vertical depth below a given datum.


A break in the succession of sedimentary deposition, commonly associated with erosion of underlying rock units. Often marked by rock surfaces which are non-parallel above and below the unconformity.


Associated with an estimate of possible hydrocarbons for which a discount attributable to risk has not been applied.


Toward a higher elevation on a rock surface.


Elevation by means of geological activity of one surface or area relative to another.

Well log

A device which records rock physical parameters in the well bore during or after drilling, or, the data obtained by these devices.

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