Oil and Gas Terms Beginning with “A” — Page 4

Afterflow is the continued influx of reservoir fluid from the formation into the wellbore during the period immediately after a well is shut in at the surface during a pressure transient test. When the surface valve… Read more →

Aggradation is the stratigraphic process by which a sedimentary sequence accumulates through vertical stacking of depositional units, occurring when the rate of sediment supply approximately equals the rate at which… Read more →

Aggregation in drilling fluid technology is the process by which suspended clay particles, principally smectite and mixed-layer illite-smectite platelets, are forced into compact face-to-face stacks by the compression… Read more →

Air drilling is a drilling technique in which compressed air, nitrogen, natural gas, or a mixture of gas and water or surfactant replaces conventional liquid-based drilling fluid as the primary circulating medium for… Read more →

An air gun is a pneumatic seismic source device that stores a volume of compressed air at high pressure (typically 1,500 to 2,000 psi, or 103 to 138 bar) and releases it instantaneously into the surrounding water… Read more →

Air shooting, also known as the Poulter method, is a seismic acquisition technique in which explosive charges are detonated in free air above the ground surface rather than in drilled shot holes, generating elastic… Read more →

An air wave is a pressure disturbance that propagates through the atmosphere at the local speed of sound after a seismic energy source fires, recording on land seismic receivers (geophones or MEMS accelerometers) as a… Read more →

An alias filter is a low-pass electronic or digital filter applied to a continuous signal before it is sampled at a discrete rate, with the specific purpose of removing all frequency components above the Nyquist… Read more →

Aliasing is the signal distortion that occurs when a continuous signal is sampled at a rate insufficient to capture its full frequency content, causing signal components at frequencies above the Nyquist frequency (f N =… Read more →

An alidade is a telescopic sighting instrument mounted on a flat straightedge base, used in conjunction with a plane table to perform topographic and geological field surveys by determining the direction, horizontal… Read more →

An aliphatic compound is any organic molecule in which carbon atoms are arranged in straight chains, branched chains, or non-aromatic ring structures, as opposed to the planar, fully conjugated ring systems that define… Read more →

In oil and gas operations, alkaline describes any aqueous solution or solid material with a pH greater than 7.0, meaning the molar concentration of hydroxide ions [OH - ] exceeds the molar concentration of hydrogen ions… Read more →

Alkaline flooding is an enhanced oil recovery (EOR) technique in which an alkaline chemical, most commonly sodium carbonate (Na 2 CO 3 ), sodium hydroxide (NaOH), or sodium orthosilicate (Na 2 SiO 3 ), is injected into… Read more →

Alkaline-surfactant-polymer (ASP) flooding is a three-component chemical enhanced oil recovery (EOR) technique that combines an alkaline agent, a synthetic surfactant, and a water-soluble polymer into a single injected… Read more →

Alkalinity is the quantitative measure of a solution's capacity to neutralise acids, expressed in terms of the equivalent concentration of calcium carbonate (mg CaCO 3 /L or equivalents per litre) that would be required… Read more →

The alkalinity test is the standardised titration procedure used at the well site and in oilfield laboratories to measure the acid-neutralising capacity of a drilling fluid filtrate, whole mud sample, completion fluid,… Read more →

An allochthon is a body of rock that has been transported a significant distance from its original site of formation by tectonic displacement (thrust faulting, nappe emplacement), gravity-driven sliding, or… Read more →

Allochthonous is the adjective describing any material — rock mass, mineral, organic matter, or sediment body — that originated or formed at a different location from where it is now found, having been transported to… Read more →

Allogenic describes any mineral grain, rock fragment, or sedimentary component that originated at a location external to the depositional basin and was transported to its current position by physical processes (wind,… Read more →

Alluvial is the adjective describing any geological feature, depositional environment, sediment body, or rock unit formed by the action of flowing surface water — rivers, streams, and ephemeral wash — on land, above the… Read more →

Alluvium is the collective noun for all unconsolidated or poorly lithified sedimentary material deposited by flowing surface water — rivers, streams, and flood events — on land above the permanent influence of marine,… Read more →

Alpha processing is a signal-combination technique in petrophysical log interpretation that merges two measurements of the same formation property — one that provides high accuracy but coarse vertical resolution, and… Read more →

The altered zone is the near-wellbore annular region of formation rock, extending typically 2 to 30 centimetres from the borehole wall into the undisturbed formation, in which acoustic velocity, mechanical properties,… Read more →

Alum refers to two closely related aluminum sulfate compounds used in the oil and gas industry: potassium alum (KAl(SO₄)₂·12H₂O, molecular weight 474.4 g/mol), the crystalline double sulfate of potassium and aluminum… Read more →

The aluminum activation log is a nuclear logging measurement that identifies aluminum-bearing minerals in the formation by neutron activation of stable aluminum-27: fast neutrons from a downhole chemical source… Read more →

Aluminum stearate is a metallic soap formed by the reaction of aluminum hydroxide Al(OH)₃ with stearic acid (octadecanoic acid, C₁₇H₃₅COOH, a saturated C18 fatty acid derived from tallow or palm oil), producing the… Read more →

Ambient temperature in petroleum engineering refers to the temperature of the local environment surrounding a piece of equipment, structure, or wellsite facility, distinct from process fluid temperatures, subsurface… Read more →

Amides are organic compounds containing the amide functional group, in which a carbonyl carbon (-C=O) is bonded directly to a nitrogen atom: primary amides have the structure R-CO-NH₂, secondary amides (also called… Read more →

Amines are organic compounds derived from ammonia (NH₃) by replacement of one, two, or three hydrogen atoms with organic substituents: primary amines (R-NH₂), secondary amines (R₂NH), and tertiary amines (R₃N) contain… Read more →

Amplitude in seismic exploration refers to the maximum absolute value of a seismic trace signal at a given two-way travel time, representing the strength of the reflection returned from a subsurface interface between… Read more →