Oil and Gas Terms Beginning with “A” — Page 6

An antithetic fault is a secondary fault whose sense of displacement is opposite to that of the major, or synthetic, fault with which it is associated. In a normal fault system where the master fault dips to the east,… Read more →

An antiwhirl bit is a polycrystalline diamond compact (PDC) drill bit engineered with an asymmetric cutter layout and stabilizing geometry that creates a controlled net lateral force, preventing the bit from orbiting… Read more →

Aperture is a term used in two distinct but related contexts in petroleum geoscience and engineering: in seismic acquisition and processing , aperture refers to the spatial extent of a receiver array or the range of… Read more →

Apparent anisotropy is a seismic velocity measurement that quantifies the ratio of the normal-moveout (NMO) stacking velocity to the true vertical interval velocity derived from well logs or a vertical seismic profile… Read more →

Apparent dip is the angle that a planar geological feature, such as a bedding surface, fault plane, or unconformity, makes with the horizontal when that angle is measured in any vertical cross-section that is not… Read more →

Apparent matrix is a petrophysical concept describing the effective solid-framework properties calculated by combining two or more porosity-sensitive log measurements to determine the mineral composition of a formation.… Read more →

Apparent velocity is the speed at which a seismic wavefront appears to travel along a surface or along a seismic recording line, as opposed to the true velocity at which the wave travels through the subsurface medium.… Read more →

Apparent viscosity (AV) is the calculated resistance to flow of a drilling fluid or completion fluid at a specific shear rate, expressed in millipascal-seconds (mPa·s), which are numerically identical to centipoise… Read more →

What Is Apparent Wavelength? Apparent wavelength is the distance between successive zero-crossings, or equivalently between successive peaks, of a wave as measured along a receiver line when that wavefront arrives at an… Read more →

In petroleum operations, appraisal is the phase that bridges a successful exploration discovery and a committed development program. Once a wildcat or exploration well encounters a potentially commercial hydrocarbon… Read more →

An aquifer is any subsurface rock formation that contains and transmits groundwater in commercially or practically significant quantities. In petroleum operations, the term carries two distinct but related meanings.… Read more →

What Is Area Open to Flow? Area open to flow (AOF) is the total cross-sectional area of the perforation tunnels connecting a producing reservoir to the wellbore . It is calculated as the number of active perforations… Read more →

Areal displacement efficiency (E A ) is the fraction of the total pattern area within a waterflood or enhanced oil recovery (EOR) project that has been contacted, or swept, by the injected fluid at the time of… Read more →

Arenaceous is the adjective applied to any rock or sediment whose texture is dominated by grains in the sand-size range, defined by the Wentworth scale as particles measuring between 62.5 micrometers (0.0625 mm) and 2… Read more →

Argillaceous is the adjective applied to any rock or sediment that contains a significant proportion of particles smaller than 62.5 micrometers (0.0625 mm) in diameter, encompassing both the silt fraction (3.9 to 62.5… Read more →

A mathematical method of finding a central value for a group of data. It is most often referred to as the average but also as the mean. The arithmetic mean is the sum of all the observed values divided by the number of… Read more →

Armor refers to the outer layers of helically wound metal wire strands that encase a wireline logging cable, providing the mechanical strength needed to support the cable and its attached logging tools during descent… Read more →

The aromatic content test is a standardized analytical procedure used to quantify the percentage of aromatic hydrocarbons present in petroleum-derived and synthetic base oils intended for use in oil-base and… Read more →

An aromatic hydrocarbon is a cyclic organic compound whose molecular structure contains at least one benzene ring, characterized by a planar, fully conjugated system of delocalized pi (π) electrons that satisfies… Read more →

In computing, code written to access data in more than one dimension according to a name and subscripts that correspond to each dimension. Read more →

An array induction tool is an electromagnetic wireline logging instrument that simultaneously acquires multiple induction measurements at different depths of radial investigation into a formation, then applies digital… Read more →

An array laterolog is a focused-current wireline logging instrument that uses multiple electrode arrays to measure formation resistivity at several simultaneous depths of radial investigation, delivering the true… Read more →

Array propagation resistivity is a logging-while-drilling (LWD) measurement technique that determines formation resistivity by transmitting electromagnetic waves into the surrounding rock and measuring the wave's… Read more →

An array sonic tool is a multi-receiver wireline or LWD logging instrument that records compressional (P-wave), shear (S-wave), and Stoneley wave acoustic modes simultaneously from an array of spatially separated… Read more →

What Is Arrival in Oil and Gas Drilling? In oil and gas drilling, arrival refers to the moment a drill bit reaches a specific target, whether that is a predetermined depth, a target formation, a stratigraphic marker, or… Read more →

Arrival time is the elapsed time between the firing of a seismic or acoustic source and the detection of a wave at a receiver. It is the foundational measurement in both surface seismic exploration and downhole acoustic… Read more →

What Is Artificial Intelligence in Oil and Gas? Artificial intelligence (AI) in oil and gas refers to the application of machine learning algorithms, deep neural networks, computer vision, natural language processing,… Read more →

What Is Artificial Lift? Artificial lift encompasses any mechanical, hydraulic, or pneumatic system that supplements natural reservoir energy to move produced fluids from the formation to the surface when reservoir… Read more →

As-delivered BTU is the heating value of a natural gas stream as measured at the precise point where custody transfers from seller to buyer, accounting for the actual composition, temperature, and pressure of the gas at… Read more →

The number of BTUs in a cubic foot of natural gas. The natural gas heat energy (BTU) will depend mainly on its water content at the delivered pressure and temperature conditions. Read more →