Oil and Gas Terms Beginning with “D” — Page 3

A series of gravity measurements made along a line or over an area of a locally high topographic feature to remove or compensate for the effect of topography on deeper density readings. Read more →

A departure curve in wireline logging analysis is a graph or chart that shows the departure (deviation) of a measured log value from the value that would be expected for the same formation at the same depth if no… Read more →

Dephasing in nuclear magnetic resonance (NMR) logging is the loss of phase coherence among the ensemble of hydrogen proton spins precessing about the static magnetic field after they have been tipped into the transverse… Read more →

An isolated section of reservoir in which the pressure has dropped below that of adjacent zones or the main body of the reservoir formation. Read more →

What Is Depletion? Depletion (also referred to as reservoir depletion or the depletion allowance) describes two related concepts that are central to oil and gas operations: the physical progressive decline in reservoir… Read more →

A deployment system in oil and gas well operations is the integrated mechanical assembly used to convey, position, and retrieve downhole tools, equipment, or completion components within the wellbore — encompassing the… Read more →

The area of thickest deposition in a basin. Read more →

The action of moving sediments and laying them down. Read more →

Depositional energy is the kinetic energy of the transporting medium (water, wind, or ice) present at the time and place that sedimentary particles were deposited, which determines the grain size, sorting, sedimentary… Read more →

What Is a Depositional Environment? Depositional environment (also called sedimentary environment or facies environment) is the physical, chemical, and biological setting in which sediment accumulates, encompassing… Read more →

A depositional system is an assemblage of genetically linked sedimentary environments, processes, and facies that are connected by active sediment transport pathways and function together as a three-dimensional body of… Read more →

The practice of ensuring that all measurements taken in a borehole are matched to the "base depth," normally the depth determined with the resistivity log. Read more →

A device used in acquisition of marineseismic data that keeps streamers at a certain depth in the water. Read more →

Depth conversion is the process of transforming seismic reflection data from the time domain (in which it is acquired, with seismic two-way travel time in milliseconds as the vertical axis) to the depth domain (with… Read more →

The process of comparing and fixing measured depths with known features on baseline logs of the wellbore tubulars and the surrounding formation. Read more →

(noun) A fixed reference elevation from which all depth measurements in a well are calculated, typically the kelly bushing, rotary table, drill floor, or mean sea level. Establishing a consistent depth datum is… Read more →

A two-dimensional representation of subsurface structure with contours in depth that have been converted from seismic traveltimes. Read more →

A depth mark in wireline logging is a magnetic mark physically placed on a wireline logging cable at regular intervals during cable manufacturing — providing a precise depth reference system that supports the depth… Read more →

What Is Depth Matching in Well Logs? Depth matching is the process of aligning two or more wireline or LWD log runs from the same wellbore to a common depth scale by applying depth shifts to one or more runs based on… Read more →

Depth matching is the practice of systematically shifting the depth scales of different subsurface data sets — wireline logs, LWD logs, cores, borehole seismic, and other measurements — to align them to a common depth… Read more →

Depth migration is a seismic data processing technique that repositions reflected seismic energy to its true spatial location in depth (in meters or feet below a datum), using an accurate velocity model of the… Read more →

Depth of invasion is the radial distance from the borehole wall into the surrounding permeable formation to which drilling fluid filtrate has displaced original formation fluids, creating a series of concentric zones:… Read more →

What Is Depth of Investigation? Depth of investigation (DOI) is the radial distance from the borehole axis at which a wireline or LWD logging tool is primarily sensitive to formation properties. It defines how far into… Read more →

A point on the surface for which the depth to a horizon has been calculated in a refractionseismic survey. The term is commonly misused as a synonym for common depth point. Read more →

A depth reference is the fixed surveyed datum from which all wellbore depth measurements are recorded, with common references including kelly bushing (KB) elevation, rotary table (RT) elevation, ground level (GL), mean… Read more →

A point within the wellbore from which accurate depth measurements can be made, such as the end of the tubing string, or a nipple or similar completion component. Read more →

A display of seismic data with a scale of units of depth rather than time along the vertical axis. Careful migration and depth conversion are essential for creating depth sections. Read more →

A depth wheel is a mechanical or electromechanical device mounted on the wireline sheave or cable drum system that measures the length of wireline cable that has been paid out from the surface unit, generating depth… Read more →

What Is Depth-Derived? A depth-derived measurement in well logging and drilling engineering is any quantity computed from measured depth (MD) along the wellbore trajectory using directional survey data, including true… Read more →

Derivative logs in pressure transient analysis are plots of the logarithmic derivative of wellbore pressure with respect to the natural logarithm of time (or the equivalent Bourdet derivative with respect to log of… Read more →