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

Interstitial water (also called connate water, formation water, or irreducible water) is the water that occupies a portion of the pore space of a reservoir rock and cannot be displaced by oil or gas because it is held… Read more →

The interval method is a specialized technique for improving the accuracy and vertical resolution of injection profile measurements obtained using the velocity-shot method in production logging — providing the… Read more →

The elapsed time between two seismic events. Read more →

Interval transit time (Δt, pronounced "delta-t") is the sonic log measurement representing the time required for a compressional acoustic wave to travel one foot through the formation — expressed in microseconds per… Read more →

Interval velocity describes the propagation speed of a seismic wave, typically a compressional or P-wave, through a discrete rock layer or stratigraphic interval, and it is symbolized as vint in the geophysics… Read more →

What Is the Invaded Zone? Invaded zone (also called the flushed zone or the zone of invasion, depending on the degree of displacement) is the region of formation rock surrounding a wellbore where the original formation… Read more →

Invasion in petroleum well logging and formation evaluation refers to the process by which drilling fluid filtrate (the liquid phase of the drilling mud that passes through the mudcake on the wellbore wall under 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 →

An inverse filter in well logging signal processing is a finite impulse response (FIR) digital filter that has been mathematically designed to transform the typically irregular vertical response functions of raw logging… Read more →

The inverse problem in geophysics is the mathematical challenge of inferring the subsurface model parameters (velocity, density, impedance, resistivity, or susceptibility) that produced a set of observed geophysical… Read more →

Seismic inversion is the mathematical process of transforming seismic reflection data into quantitative rock property models of the subsurface — specifically converting the relative amplitude information encoded in… Read more →

An invert emulsion oil mud (also called invert emulsion mud, oil-based mud, or OBM) is a drilling fluid in which oil (typically diesel, mineral oil, or synthetic base oil) is the continuous external phase and water… Read more →

An invert emulsion oil mud (also called invert emulsion mud, oil-based mud, or OBM) is a drilling fluid in which oil (typically diesel, mineral oil, or synthetic base oil) is the continuous external phase and water… Read more →

An invert emulsion oil mud (also called invert emulsion mud, oil-based mud, or OBM) is a drilling fluid in which oil (typically diesel, mineral oil, or synthetic base oil) is the continuous external phase and water… 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 →

Ion exchange in oil and gas drilling is a reversible chemical process in which cations (typically sodium, calcium, magnesium, potassium, or hydrogen ions) are swapped between the aqueous phase of a drilling fluid and… Read more →

Iron oxide is a class of mineral and inorganic compounds composed of iron in either +2 (ferrous) or +3 (ferric) valence states bonded with oxygen in the -2 valence state — including the principal iron oxides ferrous… Read more →

What Is Iron Sulfide? Iron sulfide is a group of iron-sulfur compounds, principally ferrous sulfide (FeS), ferric sulfide (Fe2S3), and iron disulfide (FeS2), that form as drilling fluid contaminants from reaction… Read more →

Iron-oxidizing bacteria (IOB) are a group of microorganisms that obtain energy by catalyzing the oxidation of ferrous iron (Fe²+) to ferric iron (Fe³+) — using the energy released by this chemical reaction as a… Read more →

Irreducible water saturation (Swi or Swirr) is the lowest water saturation that can be achieved in a core plug by displacing the water with oil or gas under controlled laboratory conditions — typically established by… Read more →

An isochore is a contour map or line of equal true vertical thickness of a geological formation, interval, or fluid column, drawn in the subsurface by subtracting the true vertical depth (TVD) of the base of the… 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 →

What Is an Isochronal Test? Isochronal test (from the Greek isochronos , meaning equal time) is a gas well deliverability testing method designed specifically for low-permeability reservoirs where the stabilization of… Read more →

Isolated porosity is the fraction of a rock's total pore volume that is not hydraulically connected to the surrounding pore network, meaning the fluid it contains cannot flow to a wellbore under normal production… Read more →

Isomerized olefin (IO) is a synthetic base fluid for drilling muds derived from olefins (alkenes with carbon-carbon double bonds) that have been isomerized — chemically rearranged to branch the carbon chain and remove… Read more →

An isopach is a contour line on a map that connects points of equal true stratigraphic thickness of a rock unit (formation, member, bed, or reservoir interval), drawn to represent the spatial variation in depositional… Read more →

Isopropanol, also called isopropyl alcohol or IPA, is a simple secondary alcohol with the molecular formula C3H8O (sometimes written C3H7OH), a molecular weight of 60.10 g/mol, and a boiling point of 82.6 degrees C… Read more →

Isostasy in petroleum geology and basin analysis is the gravitational equilibrium principle by which the Earth's lithosphere floats on the denser, viscous mantle such that topographic and density loads at the surface… Read more →

An isostatic correction is an adjustment applied to gravity data to remove the gravitational effect of the deep mass that compensates for variations in the density or thickness of the Earth's crust. The correction rests… Read more →