Oil and Gas Terms Beginning with “A” — Page 5

A amplitude anomaly is an abrupt departure from the background amplitude level observed in a seismic dataset that cannot be explained by structural, stratigraphic, or processing artifacts alone. In practice, the term is… Read more →

What Is Amplitude Variation with Offset? Amplitude variation with offset (AVO) describes the systematic change in seismic reflection amplitude as the distance between a seismic source and receiver increases, revealing… Read more →

In petroleum engineering and microbiology, anaerobic refers to any system, chemical reaction, or biological process that proceeds in the complete absence of free molecular oxygen (O₂). Anaerobic conditions are the norm… Read more →

In petroleum geology and reservoir engineering, an analog is a well-characterized geological setting, producing field, or surface outcrop that is used as a reference model to predict the properties, behavior, and… Read more →

The angle of approach is the acute angle formed between an incoming seismic ray and the reflecting or refracting interface itself at the point of intersection. Because the interface and its normal are perpendicular to… Read more →

The angle of incidence is the acute angle formed between an incoming seismic ray and the normal (perpendicular) to a reflecting or refracting interface at the point of intersection. It is conventionally measured in… Read more →

Angular dispersion is the variation of seismic wave velocity as a function of propagation direction, encompassing both azimuth (compass bearing within the horizontal plane) and dip (angle from vertical). In a… Read more →

An angular unconformity is a buried erosional surface that separates a younger sequence of sedimentary strata from an older sequence whose bedding planes dip at a measurably different angle. The angular discordance… Read more →

Anhydrite is the anhydrous (water-free) mineral form of calcium sulfate, with the chemical formula CaSO 4 . It belongs to the orthorhombic crystal system and forms transparent to white, gray, or pale blue crystals with… Read more →

The aniline point test is a standardized laboratory procedure defined by ASTM D611 that measures the minimum temperature at which equal volumes of aniline and a petroleum oil become completely miscible, forming a single… Read more →

An anion is an ion that carries a net negative electric charge, formed when a neutral atom or molecule gains one or more electrons. In the context of oil and gas operations, anions are central to the electrochemical… Read more →

An anisotropic formation is a subsurface rock body whose physical properties vary with the direction of measurement. In an isotropic material, a wave or fluid traveling through the rock encounters the same resistance,… Read more →

(noun) The directional dependence of a physical property, such that measurements yield different values when taken along different axes. In petroleum geoscience, anisotropy in permeability, seismic velocity, and… Read more →

An annubar is a multi-port averaging Pitot tube flow meter inserted across the full diameter of a pipe to measure the volumetric or mass flow rate of gases, liquids, or multiphase streams in pipelines and process… Read more →

What Is an Annular Blowout Preventer? An annular blowout preventer seals the wellbore around any tubular size or open borehole by hydraulically squeezing a toroidal elastomeric packing element radially inward against… Read more →

Annular flow is a multiphase flow regime in which a continuous film of the heavier fluid (typically liquid) coats the inner wall of the pipe while the lighter fluid (typically gas) occupies the central core at high… Read more →

Annular gas flow (AGF) is the migration of formation gas through the annular space between a casing string and the borehole wall, typically through or around the cement sheath that is supposed to provide a hydraulic… Read more →

Annular pressure is the fluid pressure acting within the annular space between two concentric tubular strings inside a wellbore. That space may exist between the drill pipe and the open formation or between drill pipe… Read more →

Annular production is the production of hydrocarbons or formation fluids through the annular space between the production tubing string and the innermost casing string, rather than through the bore of the production… Read more →

The annular space is the ring-shaped (toroidal) void that exists between two concentric cylindrical objects placed one inside the other. In drilling and well construction, this term describes the space between the outer… Read more →

Annular velocity (AV) is the linear speed at which a fluid travels through the annular space between two concentric cylinders, specifically the space between the drill string and the borehole wall or casing string… Read more →

(noun) The plural form of annulus. In well construction, annuli refers to the multiple concentric annular spaces formed between successive strings of casing, or between the innermost casing or tubing and the wellbore… Read more →

The annulus is the ring-shaped space between two concentric cylindrical objects inside a wellbore . In oil and gas well construction, the term describes any gap that exists between an inner pipe string and either an… Read more →

What Is an Anode in Oil and Gas? An anode is a sacrificial or impressed-current electrode that drives protective electrochemical current onto a steel structure, preventing the electrolytic corrosion that would otherwise… Read more →

What Is an Anomaly in Oil and Gas Exploration? An anomaly in petroleum geoscience is an observed value of any physical, chemical, or geological property that deviates measurably from an expected background level,… Read more →

Anoxic describes an environment in which free dissolved oxygen is absent or reduced to negligible concentrations, generally below 0.2 millilitres per litre (mL/L) of water. The term derives from the Greek prefix an-… Read more →

An anticlinal trap is a type of structural hydrocarbon trap whose closure is controlled by the geometry of an anticline. Oil and gas accumulate beneath the crest of the anticline because hydrocarbons, being less dense… Read more →

An anticline is an arch-shaped fold in rock in which the strata are upwardly convex, meaning the layers curve upward toward a central high point. The oldest rocks occupy the core of an anticline, while progressively… Read more →

An antifoam agent is a surface-active chemical additive used to prevent or suppress the formation of foam in drilling fluids , cement slurries, completion fluids , and other treatment fluids mixed or pumped at the… Read more →

The antisqueeze effect is a borehole measurement artifact that occurs in laterolog resistivity tools when a high-resistivity formation bed is bounded above and below by low-resistivity beds. Under this specific… Read more →