Oil and Gas Terms Beginning with “A” — Page 3

Acoustic emission (AE) is the generation of transient elastic waves produced within a material when energy is released rapidly from localized sources such as microcrack initiation, crack propagation, grain boundary… Read more →

Acoustic impedance (Z) is the product of a rock's bulk density (rho) and the compressional wave velocity (Vp) through that rock: Z = rho × Vp. It is expressed in units of kg/(m²s), sometimes written as rayl (SI unit) or… Read more →

An acoustic impedance section is a two-dimensional or three-dimensional seismic display in which the horizontal axis represents lateral position and the vertical axis represents depth or two-way travel time, but where… Read more →

The acoustic log is a wireline or logging-while-drilling (LWD) measurement of an acoustic property of the subsurface formation or the borehole, recorded as a function of depth. The most common acoustic log measurement… Read more →

An acoustic mode is a specific pattern of elastic wave propagation in which acoustic energy travels through or along a medium in a characteristic waveform pattern, with its own velocity, spatial distribution, and… Read more →

Acoustic positioning is a method of determining the underwater position of marine equipment by measuring the travel time of acoustic signals between a known reference point and the object to be located, then converting… Read more →

An acoustic transducer is a device that converts electrical energy into acoustic (sound) energy when acting as a transmitter, and converts incoming acoustic pressure variations back into electrical signals when acting… Read more →

Acoustic transparency describes the condition of a geological formation or body of material whose acoustic impedance (the product of density and P-wave velocity) is spatially uniform throughout its volume, so that… Read more →

An acoustic wave is a mechanical disturbance that propagates through a medium by alternately compressing and expanding adjacent volumes of material, transmitting energy from one point to another without net transport of… Read more →

Seismic acquisition is the process of generating controlled acoustic energy at or near the earth's surface (or seafloor), measuring the reflected and refracted wavefields at arrays of receivers distributed across the… Read more →

An acquisition log is the wireline or logging-while-drilling (LWD) record that is physically recorded in the field at the time the measurement is made, as opposed to the final processed log delivered to the operator… Read more →

An acrylamide-acrylate polymer is a linear synthetic polymer chain built from two types of monomer units: nonionic acrylamide (CH2=CH-CO-NH2) and anionic acrylate (CH2=CH-COO- Na+). The proportion of each monomer in the… Read more →

An acrylamide polymer is a synthetic polymer built from acrylamide monomers (CH2=CH-CO-NH2), forming linear or slightly branched chains with a nonionic character at neutral to mildly alkaline pH because the amide group… Read more →

Acrylamide-acrylate polymer in its partially hydrolyzed polyacrylamide (PHPA) form is the most widely deployed shale inhibitor and clay encapsulant in water-base drilling fluid programs across the Western Canada… Read more →

Acrylamido-methyl-propane-sulfonate polymer, commonly abbreviated AMPS polymer, is a synthetic polymer containing 2-acrylamido-2-methylpropane sulfonic acid (AMPS) monomer units, either as a homopolymer or, more… Read more →

Acrylamido-methyl-propane-sulfonate polymer (AMPS polymer) in its application as a cement fluid loss additive represents a distinct and technically critical use case from its role as a drilling fluid viscosifier and… Read more →

An acrylate polymer is a synthetic polymer built from acrylic acid monomers (CH2=CH-COOH) or their salts (sodium acrylate, CH2=CH-COO-Na+), forming fully anionic linear chains in which every repeat unit carries a… Read more →

An activation log is a cased-hole nuclear measurement that bombards the formation with fast neutrons from an electronic neutron generator and records the characteristic gamma rays emitted by specific elements as they… Read more →

An active margin is a continental or oceanic plate boundary at which two tectonic plates converge, producing ongoing seismicity, volcanism, and crustal deformation that distinguish it from the geologically quieter… Read more →

The thermodynamic activity of water in an aqueous solution (written a_w) is a dimensionless measure of the effective concentration of water molecules available to participate in chemical or physical processes, equal to… Read more →

Additivity is a mathematical property of geostatistical semivariogram models stating that any linear combination of valid variogram model functions with non-negative weights is itself a valid (positive semi-definite)… Read more →

Adhesion tension (AT) is the net force per unit length acting on a solid surface at the three-phase contact line where two immiscible fluids (such as oil and water) and a solid surface meet simultaneously, defined as… Read more →

An adjustable choke is a variable-area flow restriction device installed at the wellhead or in the production flowline to control the rate of fluid production from an oil or gas well by changing the size of the aperture… Read more →

Adjusted flow time, also called equivalent producing time or effective flowing time, is the single calculated value of constant-rate production time that would generate the same cumulative depletion of reservoir… Read more →

Adsorbed gas is natural gas (primarily methane) that is held on the internal surfaces of a porous solid material by intermolecular attractive forces rather than existing as a free compressible gas phase in the open pore… Read more →

Adsorption is the accumulation of molecules from a fluid phase (gas or liquid) onto the surface of a solid material, forming a concentrated molecular layer at the solid-fluid interface, driven by the reduction of… Read more →

Advective transport modeling is the quantitative description of the movement of dissolved or suspended substances through porous rock by the bulk flow of the carrier fluid (advection), as distinct from the slower mixing… Read more →

The aerated layer is the near-surface zone of unconsolidated or poorly consolidated sediment in which pore space is occupied by air rather than liquid water, causing compressional-wave (P-wave) seismic velocities to… Read more →

Aerobic refers to conditions, processes, or organisms that require free molecular oxygen (O2) for metabolic activity, contrasted with anaerobic conditions in which oxygen is absent or excluded. In oilfield operations,… Read more →

An aeromagnetic survey is the systematic airborne measurement of variations in the total intensity of Earth's magnetic field across a study area, using a magnetometer mounted on or towed beneath a fixed-wing aircraft or… Read more →