Oil and Gas Terms Beginning with “A”

An A-leg is one of the two or more separate wellbore branches in a multilateral well or one of the parallel piping paths in a dual-completion or production manifold system. In multilateral drilling, the main wellbore is… Read more →

What Is an AFE? An AFE, or Authority for Expenditure, is the budget approval document an oil and gas operator sends before spending joint-account money on a specific job. It turns a drilling, completion, workover, or… Read more →

AGC, or Automatic Gain Control, is a signal-processing technique in which the amplification applied to a recorded waveform is continuously and automatically adjusted so that the output amplitude remains within a defined… Read more →

The AGC time constant, more precisely called the AGC gate length or AGC window length, is the duration of the sliding time window over which root-mean-square (RMS) amplitude energy is computed during automatic gain… Read more →

Drilling deep used to be brutal on chemistry. Below 3,500 metres in Western Canada, the rock at the bottom of a horizontal well runs 140 to 180°C. The mud pumped down there has to stay thick, build a filter cake, and… Read more →

AOF , or Absolute Open Flow , is the theoretical maximum rate at which a gas well would produce if the flowing bottomhole pressure (BHFP) were reduced to atmospheric pressure (approximately 0.101 MPa). It is not a rate… Read more →

AOFP , or Absolute Open Flow Potential , is the theoretical maximum rate at which a gas or gas-condensate well would produce if the bottomhole flowing pressure were reduced to atmospheric pressure (approximately 101… Read more →

API stands for the American Petroleum Institute , the principal trade association and technical standards body for the United States oil and natural gas industry, founded in 1919 and headquartered in Washington, D.C. In… Read more →

API Specification 10A (formally titled "Specification for Cements and Materials for Well Cementing," also referred to as API Spec 10A and harmonised internationally with ISO 10426-1 ) is the American Petroleum Institute… Read more →

API cement is oilfield cement manufactured to the dimensional, chemical, and physical performance requirements specified in API Specification 10A (equivalent to ISO 10426-1:2009), the American Petroleum Institute… Read more →

API gravity is a specific gravity scale developed by the American Petroleum Institute (API) and the National Institute of Standards and Technology (NIST) that expresses the density of crude oil and petroleum liquids… Read more →

The API unit (symbol: gAPI ) is the internationally standardised unit of measurement for natural gamma ray radioactivity in wellbore logging, established by the American Petroleum Institute to provide a universal… Read more →

API water is the precisely defined quantity of mixing water prescribed by API Specification 10A (and its ISO equivalent ISO 10426-1) for preparing oilwell cement test slurries in laboratory conditions. The designation… Read more →

ASTM International (originally the American Society for Testing and Materials, founded in Philadelphia in 1898) is a globally recognised standards development organisation that publishes voluntary consensus technical… Read more →

Annular velocity (AV), sometimes abbreviated as AV in drilling engineering documentation and mud reports, is the linear speed at which drilling fluid flows upward through the annular space between the outside of the… Read more →

AVO, an acronym for Amplitude Variation with Offset , describes the systematic change in the amplitude of a seismic reflection as the source-to-receiver offset (distance) increases in a seismic survey, caused by the… Read more →

An agitator in drilling operations is a mechanical, pneumatic, or jet-driven device installed in or on active mud pits, suction pits, mixing pits, or reserve pits to maintain drilling fluid in a continuously mixed,… Read more →

An air compressor used in drilling operations is a mechanical device that increases the pressure of atmospheric air (or, in sensitive formations, nitrogen or natural gas) from ambient conditions to the elevated… Read more →

An air hoist, also called a pneumatic hoist, is a lifting device powered by compressed air in which the energy of pressurised air drives a rotary air motor to wind a wire rope or lift a roller chain, raising and… Read more →

Alford rotation is a four-component matrix processing algorithm applied to cross-dipole sonic log data that rotates the recorded shear-wave waveforms from the logging tool's physical inline and crossline polarisation… Read more →

Archie Equation is the foundational petrophysical relationship used to estimate water saturation (Sw) in a reservoir rock from wireline log measurements of electrical resistivity and porosity. First published by Gus E.… Read more →

Archie rock is a reservoir formation whose electrical properties are fully and accurately described by the Archie Equation without modification or correction for additional conduction mechanisms. The term identifies… Read more →

In the Archie formation factor equation, the symbol a (also written as A or sometimes called the tortuosity factor or lithology factor) is a dimensionless empirical coefficient that accounts for variations in pore… Read more →

Abandonment costs are the expenditures required to permanently plug and abandon a well, decommission a production facility, and restore the surface location to a condition acceptable to the regulatory authority at the… Read more →

In reflection seismic acquisition and processing, abnormal events are coherent or incoherent signals recorded on seismic traces that are not primary reflections from subsurface horizons. The term covers diffractions… Read more →

Abnormal pressure is reservoir pore fluid pressure that differs significantly from the expected hydrostatic gradient for the depth at which it occurs. Normal hydrostatic pressure increases with depth at a rate… Read more →

An abrasion test is a standardized laboratory procedure used in the oil and gas industry to measure how quickly a drilling fluid weighting material wears away metal surfaces it contacts during circulation. The test… Read more →

Abrasive jetting is a wellbore treatment in which a high-velocity slurry of fluid mixed with hard solid particles (typically sand, steel shot, or silicon carbide grit) is pumped through a nozzle and directed against the… Read more →

Absolute age is the age of a rock, mineral, or geological event measured in years (or millions of years), as distinct from relative age, which only establishes whether one rock unit is older or younger than another… Read more →

An absolute filter is a high-specification fluid filter rated by a micron size at which it achieves near-total removal (typically 99.9 percent or greater) of particles at or above that size, as distinct from a nominal… Read more →