Oil and Gas Terms Beginning with “D”

DD, an abbreviation for directional driller, refers to the specialist drilling professional responsible for planning, executing, and real-time controlling the trajectory of a directional or horizontal wellbore to guide… Read more →

A DEA unit, short for diethanolamine treating system, is a closed-loop amine absorption process that strips hydrogen sulfide (H2S), carbon dioxide (CO2), and carbonyl sulfide (COS) from raw natural gas, producing… Read more →

DMO, short for dip moveout, is the additional traveltime difference that appears in a reflected seismic wave, measured between receivers at two different source-to-receiver offsets, when the underlying reflector is not… Read more →

Distributed strain sensing (DSS) is a fiber optic monitoring technology that measures mechanical strain (the fractional change in length of a material under applied force) continuously and simultaneously along the… Read more →

A drillstem test (DST) is a well test conducted while the drill string is still in the hole, before the well is cased and completed. By packing off a zone of interest with inflatable packers or mechanically set packers… Read more →

The DST pressure chart is the continuous record of downhole pressure versus time produced by recording gauges in a drill stem test (DST) tool. As the tool is run into the hole, pressure increases steadily with depth as… Read more →

Darcy units are the system of measurement units originally used by Henry Darcy in his 1856 experiments on fluid flow through porous media, and subsequently formalized as the basis for quantifying reservoir permeability… Read more →

The drilling line from the crown block sheave to the anchor, so called because it does not move. Read more →

Dean-Stark extraction is a laboratory distillation method used to measure fluid saturations in core samples recovered from oil and gas reservoirs. By boiling a solvent through the sample and collecting the vaporized… Read more →

What Is a Decline Curve? A decline curve is a graphical and mathematical representation of the rate at which oil or gas production from a well or reservoir decreases over time — described by the Arps equations for… Read more →

Removable, hard-steel, serrated pieces that fit into the jaws of the tongs and firmly grip the body of the drill pipe, drill collars, or casing. Read more →

The power supplied to a drilling rig by diesel engines driving electric generators. Read more →

Tools utilized in achieving directional drills, including whip stocks, BHA configurations, three-dimensional measuring devices, mud motors, and specialized drill bits. Read more →

The Dix formula is an equation in seismic exploration that calculates the interval velocity (the actual propagation velocity of seismic waves within a specific layer) from the root-mean-square (RMS) velocities obtained… Read more →

What Is a Dräger Tube? A Dräger tube quantitatively measures a target gas by drawing a calibrated air sample through a glass tube packed with a reactive chemical reagent that changes colour along its length in direct… Read more →

Heavy, thick-walled tubes used between the drill pipe and the bit in the drill string, used to stiffen the drilling assembly and put weight on the bit. Read more →

What Is Drill Pipe? Drill pipe is a hollow seamless steel tubular that forms the primary structural and hydraulic connection between the surface rotary system and the downhole drill bit assembly, transmitting rotary… Read more →

A heavy duty wire rope hoisting line, reeved back and forth through the sheaves of the crown block and travelling block. Read more →

A decibel (dB) is a dimensionless unit that expresses the ratio between two quantities — power, intensity, pressure, or amplitude — on a logarithmic scale, named after Alexander Graham Bell and used throughout the oil… Read more →

What Is Formation Damage? Formation damage is any reduction in reservoir permeability in the near-wellbore region or production string caused by natural mechanisms such as fines migration and scale deposition, or… Read more →

The damaged zone (also called the damage zone or skin zone) in petroleum engineering is the region of reduced permeability immediately surrounding a wellbore — created by physical and chemical alterations to the… Read more →

Damping in oil and gas engineering refers to the dissipation of mechanical energy that reduces the amplitude of oscillations, vibrations, or pressure fluctuations in a system over time — a phenomenon with critical… Read more →

The darcy (symbol D) is the fundamental unit of permeability used in petroleum engineering and reservoir characterization — defined as the permeability of a porous medium through which a fluid with a viscosity of 1… Read more →

A device dropped or pumped through a tubing or coiled tubing string to activate downhole equipment and tools. Read more →

Data rate in MWD (measurement while drilling) and LWD (logging while drilling) systems refers to the speed at which real-time formation evaluation and directional survey data can be transmitted from the downhole tool… Read more →

A datum is a depth reference point, typically established at the time the well is completed, against which subsequent depth measurements are corrected or correlated. Every depth recorded in a well, whether a casing… Read more →

A datum correction is a value added to or subtracted from the reflection traveltimes of seismic data to compensate for the actual elevations of the geophone (receiver) and the source relative to a chosen seismic datum,… Read more →

A datum level is a single reference depth, almost always expressed as a subsea elevation, to which measured reservoir pressures are corrected so that readings taken at different elevations, in different wells, or at… Read more →

Day rate in drilling operations is the daily cost charged to the operator for renting the drilling rig along with the associated costs of personnel and routine consumable supplies — providing the foundational drilling… Read more →

Dead oil is crude that holds no dissolved gas in solution, either because it sits at a pressure low enough that all the gas has come out, or because it is a heavy, weathered oil or residue that has already lost its… Read more →