Shale Gas

Anisotropic

Having directionally dependent properties. For a crystal of a mineral, variation in physical properties observed in different directions is anisotropy. In rocks, variation in seismic velocity measured parallel or perpendicular to bedding surfaces is a form of anisotropy.

Analog

An example used for comparison. In oil and gas exploration, geoscientists and engineers compare new prospects and fields with fields and surface exposures thought to be similar in depositional environment and reservoir character to guide predictions. Wide variations in shale reservoirs create doubt about the utility of analog comparisons.

Anisotropy

Predictable variation of a property of a material with the direction in which it is measured, which can occur at all scales.

Adsorbed gas

The gas accumulated on the surface of a solid material, such as a grain of a reservoir rock, or more particularly the organic particles in a shale reservoir.

Azimuth

The direction in which a deviated or horizontal well is drilled relative to magnetic north.

Bitumen

Naturally occurring, inflammable organic matter formed from kerogen in the process of petroleum generation that is soluble in carbon bisulfide.

Basin

A depression in the crust of the Earth, caused by plate tectonic activity and subsidence, in which sediments accumulate.

Buffalo head

A flow cross installed on top of a frac tree where treating iron is connected and treatment fluid enters the frac tree.

Continuous reservoir

A type of areally extensive reservoir that contains hydrocarbon throughout, rather than containing a water contact or being significantly affected by a water column or a defined structural closure.

The physical and chemical alteration of sediments and pore fluids at temperatures and pressures higher than those of diagenesis.

Catagenesis

Conventional reservoir

A reservoir in which buoyant forces keep hydrocarbons in place below a sealing caprock.

Core analysis

aboratory study of a sample of a geologic formation, usually reservoir rock, taken during or after drilling a well.

Cummulative production

The total amount of oil and gas recovered from a reservoir as of a particular time in the life of the field. Cumulative production can be referenced to a well, a field, or a basin.

Command trailer

A trailer in which fracturing engineers can monitor formation pressures and other critical information pertaining to the fracturing process.

Composite frac tree

A frac tree in which multiple frac valves are contained in a single large body such that the overall height of the frac tree is reduced.

Completion

A generic term used to describe the events and equipment necessary to bring a wellbore into production once drilling operations have been concluded, including but not limited to the assembly of downhole tubulars and equipment required to enable safe and efficient production from an oil or gas well.

Completion quality

A prediction of how effectively rock may be stimulated using hydraulic fracturing.

Diagenesis

The initial stage of alteration of sediments and maturation of kerogen that occurs at temperatures less than 50°C [122°F].

Deviated drilling

The intentional deviation of a wellbore from the path it would naturally take.

Directional drilling

The intentional deviation of a wellbore from the path it would naturally take.

An area in which hydrocarbon accumulations or prospects of a given type occur.

Exploration play

Estimated ultimate recovery

The amount of oil and gas expected to be economically recovered from a reservoir or field by the end of its producing life. Estimated ultimate recovery can be referenced to a well, a field, or a basin.

Frac fluid

An abbreviation for fracturing fluid, a fluid injected into a well as part of a stimulation operation.

Frac head

A flow cross installed on top of a frac tree where treating iron is connected and treatment fluid enters the frac tree.

Fracture

A crack or surface of breakage within rock not related to foliation or cleavage in metamorphic rock along which there has been no movement.

Frac stack

A Christmas tree installed specifically for the fracturing process. A frac stack typically consists of upper and lower master valves, flow cross, wing valves, goat head, and swab valve. Frac stacks generally have larger bores and higher pressure ratings than production trees to accommodate the high flow rates and pressures necessary for hydraulic fracturing.

Frac job

Another term for hydraulic fracturing, a stimulation treatment routinely performed on oil and gas wells in low-permeability reservoirs. Specially engineered fluids are pumped at high pressure and rate into the reservoir interval to be treated, causing a vertical fracture to open.

Fracturing pressure

Pressure above which injection of fluids will cause the rock formation to fracture hydraulically.

That portion of a dual-porosity reservoirs permeability that is associated with the secondary porosity created by open, natural fractures. In many of these reservoirs, fracture permeability can be the major controlling factor of the flow of fluids.

Fracture permeability

Frac tree

A Christmas tree installed specifically for the fracturing process. A frac tree typically consists of upper and lower master valves, flow cross, wing valves, goat head, and swab valve. Frac trees generally have larger bores and higher pressure ratings than production trees to accommodate the high flow rates and pressures necessary for hydraulic fracturing.

A fluid injected into a well as part of a stimulation operation. Fracturing fluids for shale reservoirs usually contain water, proppant, and a small amount of nonaqueous fluids designed to reduce friction pressure while pumping the fluid into the wellbore.

Fracturing fluid

The gaseous phase present in a reservoir or other contained area.

Free gas

Formation evaluation

The measurement and analysis of formation and fluid properties through examination of formation cuttings or through the use of tools integrated into the bottomhole assembly while drilling, or conveyed on wireline or drillpipe after a borehole has been drilled.

Formation evaluation while drilling

Also known as logging while drilling or LWD, the measurement of formation properties during the excavation of the hole, or shortly thereafter, through the use of tools integrated into the bottomhole assembly.

Formation fracture pressure

Pressure above which injection of fluids will cause the rock formation to fracture hydraulically.

Gas shale

Shale that produces natural gas. A shale that is thermally mature enough and has sufficient gas content to produce economic quantities of natural gas.

Geomechanics

The geologic specialty that deals with understanding how rocks, stresses, pressures, and temperatures interact.

Abbreviation for gas initially in place, the volume of gas in a reservoir before production.

GIIP

Goat head

A flow cross installed on top of a frac tree where treating iron is connected and treatment fluid enters the frac tree.

High-pressure manifold

Flow control unit used in the pressurization of fluid employed in hydraulic fracturing. Fracturing fluid enters the missile at low pressure and is directed to the pump trucks for pressurization. High-pressure fluid returns to the missile and is directed to the well or, in the case of a multiwell pad, to a frac manifold.

A stimulation treatment routinely performed on oil and gas wells in low-permeability reservoirs. Specially engineered fluids are pumped at high pressure and rate into the reservoir interval to be treated, causing a vertical fracture to open.

Hydraulic fracturing

Horizontal drilling

The intentional deviation of a wellbore from the path it would naturally take to a horizontal trajectory. Horizontal lateral sections can be designed to intersect natural fractures or simply to contact more of the productive formation.

Heterogenous

Possessing the quality of variation in rock properties with location in a reservoir or formation. 

Heterogeneity

The quality of variation in rock properties with location in a reservoir or formation. Shale gas reservoirs are heterogeneous formations whose mineralogy, organic content, natural fractures, and other properties vary from place to place.

Hydraulic fracture monitoring

A technique to track the propagation of a hydraulic fracture as it advances through a formation.

Kerogen

The naturally occurring, solid, insoluble organic matter that occurs in source rocks and can yield oil upon heating.

The measurement of formation properties during the excavation of the hole, or shortly thereafter, through the use of tools integrated into the bottomhole assembly.

Logging While Drillign (LWD)

Interstitial gas

The gas stored in the pore space of a reservoir rock. Measurement of interstitial gas and adsorbed gas, which is the gas accumulated on the surface of another solid material, such as a grain of reservoir rock, allows calculation of gas in place in a reservoir.