AN EXPLORATION GLOSSARY
OIL & GAS EXPLORATION GLOSSARY
Anticline: A fold, generally convex up-wards,
whose core contains stratigraphically
older rocks.
Core data: A solid column of rock up to
four inches in diameter taken from the well-bore
so geologists may study the rock forma-tion
for clues as to whether oil or gas is
present.
Drillstem test: A test of the productive ca-pacity of an oil or gas reservoir when the well is uncased. The test is conducted through the drill pipe to see if oil or gas is present in a certain formation; preliminary sampling aids the decision to complete or abandon the well.
Fault:A fracture or fracture zone along which the sides have been displaced relative to one another. A break or fracture in the Earth’s crust that causes rock layers to shift.
Field: An area in which a number of wells produce from a reservoir. There may be sev-eral reservoirs at various depths in a single field.
Horst: An elongate, uplifted block that is bounded by faults on its long sides.
Hydrocarbon An organic compound con-sisting of carbon and hydrogen. Hydrocar-bons
can be gaseous, liquid or solid.
Log: A continuous record as a function of depth of information on the rocks and fluids
encountered in a wellbore. The readings are commonly obtained by equipment lowered
by wireline into the wellbore. Acoustic, ra-dioactive and electrical readings are used to
identify the types of rocks and their charac-teristics. Measurement-while-drilling
(MWD) tools can accumulate data as the drill bit drills through the rock formation.
Permeability: The capacity of a rock to transmit fluids. A tight rock, sand or forma-tion
will have low permeability and thus, low capacity to produce oil or gas, unless the well
can be somehow fracture-stimulated to in-crease production. Expressed in millidarcies for tight reser-voirs and darcies for extremely permeable reservoirs.
Porosity: The volume of small to minute openings in a rock that allow it to hold fluids.
Measured in percentages, typically from near zero to about 35%. Prospect An area that is the potential site of an oil or gas accumulation. A lease or group of leases upon which an operator in-tends to drill.
Reserves: The volumes of oil and gas that can be profitably recovered from a well with existing technology and present economic conditions. Sedimentary rock A layered rock result-ing from the consolidation of sediment. Sedi-ments are materials that are transported and deposited by wind, water or ice, chemically precipitated from solution or deposited by or-ganisms.
Seismic: An earthquake or earth vibration,
including those that are artificially induced.
Strike: The direction taken by a structural
surface such as a bedding or fault plane.
Wellbore: That part of a well that is below
the surface. Hole diameters vary with the
type and purpose of wells; a common well-bore
diameter is a little less than nine inches.
(Source: Dictionary of Geological Terms,
Third Edition)
Anticline: A fold, generally convex up-wards,
whose core contains stratigraphically
older rocks.
Core data: A solid column of rock up to
four inches in diameter taken from the well-bore
so geologists may study the rock forma-tion
for clues as to whether oil or gas is
present.
Drillstem test: A test of the productive ca-pacity of an oil or gas reservoir when the well is uncased. The test is conducted through the drill pipe to see if oil or gas is present in a certain formation; preliminary sampling aids the decision to complete or abandon the well.
Fault:A fracture or fracture zone along which the sides have been displaced relative to one another. A break or fracture in the Earth’s crust that causes rock layers to shift.
Field: An area in which a number of wells produce from a reservoir. There may be sev-eral reservoirs at various depths in a single field.
Horst: An elongate, uplifted block that is bounded by faults on its long sides.
Hydrocarbon An organic compound con-sisting of carbon and hydrogen. Hydrocar-bons
can be gaseous, liquid or solid.
Log: A continuous record as a function of depth of information on the rocks and fluids
encountered in a wellbore. The readings are commonly obtained by equipment lowered
by wireline into the wellbore. Acoustic, ra-dioactive and electrical readings are used to
identify the types of rocks and their charac-teristics. Measurement-while-drilling
(MWD) tools can accumulate data as the drill bit drills through the rock formation.
Permeability: The capacity of a rock to transmit fluids. A tight rock, sand or forma-tion
will have low permeability and thus, low capacity to produce oil or gas, unless the well
can be somehow fracture-stimulated to in-crease production. Expressed in millidarcies for tight reser-voirs and darcies for extremely permeable reservoirs.
Porosity: The volume of small to minute openings in a rock that allow it to hold fluids.
Measured in percentages, typically from near zero to about 35%. Prospect An area that is the potential site of an oil or gas accumulation. A lease or group of leases upon which an operator in-tends to drill.
Reserves: The volumes of oil and gas that can be profitably recovered from a well with existing technology and present economic conditions. Sedimentary rock A layered rock result-ing from the consolidation of sediment. Sedi-ments are materials that are transported and deposited by wind, water or ice, chemically precipitated from solution or deposited by or-ganisms.
Seismic: An earthquake or earth vibration,
including those that are artificially induced.
Strike: The direction taken by a structural
surface such as a bedding or fault plane.
Wellbore: That part of a well that is below
the surface. Hole diameters vary with the
type and purpose of wells; a common well-bore
diameter is a little less than nine inches.
(Source: Dictionary of Geological Terms,
Third Edition)
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