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

A technique for improving the accuracy of injection profiles measured using the velocity-shot method. In the normal velocity-shot method, the flow velocity is determined by the time of flight of a radioactive slug… Read more →

The elapsed time between two seismic events. Read more →

The amount of time for a wave to travel a certain distance, proportional to the reciprocal of velocity, typically measured in microseconds per foot by an acoustic log and symbolized by t or DT. P-wave interval transit… Read more →

The velocity, typically P-wave velocity, of a specific layer or layers of rock, symbolized by vint and commonly calculated from acoustic logs or from the change in stacking velocity between seismic events on a common… Read more →

The volume close to the borehole wall in which some or all of the moveable fluids have been displaced by mudfiltrate. It consists of the flushed zone and the transition zone or annulus. In simple models, the invaded… Read more →

Pertaining to the influence of invasion on the response of logging measurements. For example, an invasion correction is the correction made to a deep-reading measurement such as an induction log for the effect of the… Read more →

(adjective) Describing a mathematical or analytical process in which observed data (such as seismic records, well test pressures, or production rates) are used to determine the underlying model parameters that produced… Read more →

Generally, a finite impulse response (FIR) filter that has been designed to transform the usually irregular vertical response functions of raw measurements into a smooth, well-behaved response function such as a… Read more →

The problem of determining the value or spatial variation of a physical property or feature by comparing measurements to the predictions of a model. For example, seismic traveltimes from a source to a receiver can be… Read more →

A mathematical process by which data are used to generate a model that is consistent with the data, the process of solving the inverse problem. In seismology, surface seismic data, vertical seismic profiles and well log… Read more →

An emulsion in which oil is the continuous or external phase and water is the internal phase. Invert emulsion usually refers to an oil-base mud, and the terms are considered synonyms. Invert-emulsion muds can be run… Read more →

An outdated distinction between two types of oil muds. In the past, invert-emulsion oil muds were those with more than 5 vol.% emulsified water, and oil-base muds were those with less than 5 vol.% water. Today, this… Read more →

An outdated distinction between two types of oil muds. In the past, invert-emulsion oil muds were those with more than 5 vol.% emulsified water, and oil-base muds were those with less than 5 vol.% water. Today, this… Read more →

An injection pattern in which four production wells are located at the corners of a square and the injector well sits in the center. Read more →

A process of exchanging one ion for another ion on a charged, solid substrate, such as a natural clay, zeolite or resin. Cation exchange on clay minerals occurs in muds and during mud testing. In muds, various positive… Read more →

A group of minerals and inorganic compounds made up of iron that is in +2 (ferrous) and +3 (ferric) valence states and oxygen in the -2 valence state, such as ferrous oxide, FeO, and ferric oxide, Fe2O3. Fe3O4 is a… Read more →

A group of compounds containing iron in +2 (ferrous) and +3 (ferric) valence states and sulfur in -2 (sulfide) valence states. Examples are ferric sulfide [Fe2S3], ferrous sulfide [FeS] and iron disulfide (FeS2, which… Read more →

Aerobic bacteria that convert iron from the ferrous [Fe+2] to the ferric [Fe+3] state and produce ferric hydroxide [Fe(OH)3], which is a highly insoluble by-product that will damage the formation. Iron-oxidizing… Read more →

The lowest water saturation, Swi, that can be achieved in a core plug by displacing the water by oil or gas. The state is usually achieved by flowing oil or gas through a water-saturated sample, or spinning it in a… Read more →

A contour connecting points of equal true vertical thickness of strata, formations, reservoirs or other rock units. A map that displays isochores is an isochore map. The terms isopach and isopach map are incorrectly… Read more →

A line joining points of equal time or age, such as a reflection in a seismicprofile or contours in an isochron map. Read more →

A contourmap showing the traveltimes to one particular seismic event or reflection. Read more →

A type of deliverability test conducted in gas wells. This test is used to generate a stabilized gas deliverability curve (IPR) without actually flowing the well for the time required to achieve stabilized conditions… Read more →

The pore volume not connected to the pore network. Isolated porosity can be significant in volcanic rocks and some carbonates, for example as vugular, moldic and intraparticle porosity. Read more →

A synthetic hydrocarbon liquid made by the polymerization of ethylene, H2C=CH2. IOs are one of several synthetic fluids that have recently been used as base for synthetic-base muds and in other applications where… Read more →

A contour that connects points of equal thickness. Commonly, the isopachs, or contours that make up an isopach map, display the stratigraphic thickness of a rock unit as opposed to the true vertical thickness. Isopachs… Read more →

A simple alcohol (C3H7OH) used as a solvent in some mud analyses. A 50/50 xylene/IPA mixture was used in the past as an emulsionbreaker for oil mud but has been replaced with propylene glycol normal propyl ether (PNP). Read more →

The state of gravitational equilibrium between the lithosphere and the asthenosphere of the Earth such that lithospheric plates "float" at a given elevation depending on their thickness. The balance between the… Read more →

A correction for variations in the density or thickness of the Earth's crust. Isostatic corrections are commonly applied to gravity data and are made according to a specific model for isostasy. Read more →

A type of formation whose rock properties are the same in all directions. Although this never actually occurs, fluid flow in rocks approximates this situation closely enough to consider certain formations isotropic. Read more →