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D

daily sendout requirements

The average amount of gas that an LDC must deliver to its customers daily.

daisy-chain

A wiring scheme in which the hot and/or ground leads for multiple controllers are connected through each other.

dampener

A gas or liquid-charged, chambered device that minimizes the ef¬fects of pulsation.

damper

A device consisting of one or more blades that can be adjusted to control air flow in a fan or ventilation system.

Any action that reduces the output of, or response to, sudden changes or high frequencies. In process control, adjusting the time between signal transmissions to eliminate electrical and mechanical noise, which suppresses oscillations in the process variable and slows its response to control output changes.

damping (electrical)

The process of preventing an instrument's pointer from oscillating above and below the measured value.

damping magnet

A permanent magnet used in an induction disc element that produces a fixed drag on the disc so that the disc turns at a constant speed.

DAQ

Data Acquisition.

darcy

A unit of permeability defined as that which permits a fluid of one centipoise viscosity to flow at a rate of one cubic centimeter per second through a porous medium with a cross-sectional area of one square centimeter under a pressure gradient of one atmosphere per centimeter.

data acquisition board

A plug-in printed circuit board that allows standard PCs to process input data from a variety of sensors.

data files

One of two main types of PLC files, in which the current states of inputs, outputs, timers, counters, numbers, etc. are stored.

data highway 485

An Allen-Bradley peer network for connecting members of the SLC-500 family, PCs, and low-end HMIS together.

data highway plus

An Allen-Bradley peer network for connecting members of the PLC-5 family, PCs, and high-end HMIS together.

data logger

Portable equipment typically used by maintenance personnel to take and store readings on-field equipment.

data plate

A metal plate attached to a forklift that provides important information such as the forklift's rated lifting capacity, weight and required clearances or other limitations.

data precision

Data precision refers to the closeness of two, or more, measurements to each other.

datum line

The zero point to which a liquid level measurement is referenced.

datum plate

A reference point, located near the bottom of a tank, for use in measuring liquid levels.

daughter product, daughter isotope, daughter nuclide

A daughter product, daughter isotope or daughter nuclide is the remaining nuclide left over from radioactive decay.

DC bus

A section of an AC inverter controller that serves as a reservoir of electrical energy.

DCS

Distributed Control System. A computerized network that gathers industrial process input information, makes calculations, and transmits instructions to output devices to maintain a process at desired conditions. System control is distributed across hundreds or thousands of inputs and outputs, including variable speed drives.

de-aeration

The process of removing air and non-condensable gases from condensate to decrease the amount of oxygen that is dissolved in the water.

de-aerator

A type of open feedwater heater in which steam and condensate mix together while also removing air and non-condensable gases from the condensate or water.

de-aerator storage tank

A storage tank, often located below a de-aerator, that holds de-aerated feedwater to supply the demands of the feedwater system, if needed. Also called a feedwater storage tank.

de-asphalting unit

A unit that separates recoverable oil from asphalt materials contained in pitch, or bottoms.

de-ethanizer/absorber

A tower in a cracked gas plant that receives unstabilized cat-cracked gasoline and compressed noncondensed gases from the gas recovery system. Ethanes and lighter components are removed from the top of the tower. The bottoms product is the feed stream to the debutanizer.

de-isobutanizer

See Isostripper.

dead oil

Dead oil is an oil that contains no dissolved gas or a relatively thick oil or residue that has lost its volatile components.

dead time

The time interval between when a control input or output changes and when the process or system begins to respond to that change.

dead weight tester

An instrument used to check the accuracy of the static element during an orifice meter witnessing.

deaerator

A device on the LACT unit which removes free gas and air from the oil.

debutanizer

A tower in a cracked gas plant that separates butanes and lighter components from heavier components in a feedstream. The bottoms product is stabilized cat-cracked gasoline.

decanter

An auxiliary vessel used to separate two immiscible liquids on the basis of differences in density, or a vessel in an azeotropic distillation system where overhead product separates into two liquid phases.

deceleration ramp

The time it takes for a variable speed drive to slow down from a preset speed.

decimal numbering system

The numbering system based on powers of ten.

decimal places

The places to the right of the decimal point in a decimal number.

decimal point

The period in a decimal number that separates the whole place values from the fractional place values.

declaration of inspection (DOl)

A list of requirements that must be completed before a barge transfer is performed.

declutch lever

A device that places a motor operator clutch in the manual, or handwheel, position; a clutch operating lever.

decommissioning a tank

The process of taking a storage tank out of service.

decontamination

The removal of hazardous substances from employees and their equipment to the extent necessary to preclude the occurrence of foreseeable adverse health effects.

decoupling capacitor

A compensation capacitor used to bypass power supply AC frequency variations around an op amp circuit to the ground.

defect

A characteristic of a product, such as color, shape, or size that does not match the desired or design specifications.

defective product

A product that is unusable because it has one or more defects.

defensive driving

Driving to avoid an accident in spite of adverse road, traffic, weather, vehicle, light or glare conditions, or the incorrect actions of other drivers.

degradation

Breaking down the chemical composition of amine due to high temperatures.

degrees A.P.I.

Unit of measurement that indicates the gravity or weight of oil.

dehumidifier

A device that removes moisture from air.

dehydration

The removal of water from a substance, such as natural gas or glycol.

dehydrogenation

A reforming reaction in which hydrogen is removed and a naphthene is converted to an aromatic.

delay drilling payments

An annual payment made to a property owner, typically determined by the size of the property, paid in advance of oil and gas drilling activities.

delayed gamma rays

Delayed gamma rays are the gamma rays given off by the daughter product.

delayed start

A defensive driving technique used when starting up at a stop sign or traffic light. It involves counting to three before taking your foot off the brake and then looking left, right and left again before moving.

delimiter

A punctuation mark that separates parts of an address.

delta connection

A connection in a three-phase AC system in which three coils or windings are connected end to end, with the load attached to each of the three junctions between the windings.

delta-connected stator

A stator in which the coils are connected end to end.

deluge system

A type of fire protection system that automatically dumps large amounts of water in an area in response to a fire, with valves opening due to the heat from the fire.

demand

The amount of power needed by a power system's customers.

demand-type respirator

A type of air-supplied respirator in which air is supplied to the wearer on demand as the wearer inhales.

demethanizer

A type of fractionating tower used to remove entrained methane from the liquid product of a cryogenic plant.

demister pad

A device in a distillation column that prevents entrained liquid from carrying over with the overhead product vapors.

demulsification

The process of breaking an emulsion.

demulsifier

A chemical that is added to crude to help speed up the breakdown of the water/oil emulsion in the desalter.

denitrification

A hydrotreating reaction in which hydrogen is used to remove nitrogen.

denominator

In a fraction, the number below the fraction bar, indicating how many parts a whole unit has been divided into.

dense phase

The area at the bottom of a regenerator where the greatest concentration of catalyst is located and where most of the combustion takes place.

densitometer

A device which measures the mass or weight per unit of volume.

density

The mass per unit volume of a substance (volumetric mass density).

density bubbler system

A system that measures the density of a liquid by using differential pressure.

density correction curve

The density correction curve shows how much correction has been applied to the bulk density data to compensate for borehole irregularities, rugosity and mud cake.

density porosity, density log, density logging tool

Density porosity is a formation's porosity calculated only using a density log.

department of transportation (DOT)

The U.S. government agency charged with regulating the transportation of hazardous materials.

dependent variable

In a ratio control system, the variable that is tied to a percentage of the independent variable.

depleted reservoir storage field

A depleted gas or oil field, used for storing and cycling of natural gas.

depletion region

The area along a P-N junction that is nearly depleted of electrons and holes, where electrons from the N-type material and holes from the P-type material have drifted across the junction and recombined.

depletion type MOSFET

A MOSFET that has a channel across it. Current flow through the channel is controlled by the capacitance effect between the gate and the substrate. When the gate potential is negative with respect to the source, the MOSFET is in the depletion mode. When the gate potential is positive with respect to the source, the MOSFET is in the enhancement mode.

depocenter

A basin's depocenter is an area of maximum deposition, or the geographic location of the thickest part of any specific geographic unit in a depositional basin.

depositional environment

The combination of physical, chemical, and biological processes associated with the deposition of a particular type of sediment, describing the conditions under which sediments are deposited.

depositional environment, environment of deposition

Depositional environment, or sedimentary environment, describes the combination of physical, chemical and biological processes associated with the deposition of a particular type of sediment.

depositional fabric

Depositional fabric, also known as primary fabric, is a type of “fabric” in sedimentary rocks that develops while sediment is accumulating. It results from the orientation of the crystals or grains that make up a sedimentary rock.

depropanizer

A tower that removes propane from isobutane through fractionation.

depth micrometer

A micrometer used to measure the depths of holes and recesses; accurate to the nearest .001 inch, or , 01 mm. Also called a depth gauge.

derailer

A device that fits over rails and prevents oncoming tank cars from running into a tank car spotted at a loading rack.

derivative control

A process control algorithm (sometimes called rate control) in which the control output is proportional to the rate of change of either the process variable or the error between the process variable and the set point, producing faster corrective action than proportional control alone.

derrick

The structure used to support the crown blocks and drill string of a drilling rig, usually pyramidal in shape offering a good strength-to-weight ratio. Also, any of several types of stationary cranes used primarily for lifting loads.

desalter

A component of a crude unit in which water containing salt separates from the crude and is removed.

desiccant

A drying agent or substance used to remove water, such as activated alumina, silica gel, or glycol.

design winter

The potential gas demand for the coldest winter in 50 years and the coldest historical peak 10-day period in January (Northern Hemisphere), or July (Southern Hemisphere).

designated area

An area that may be used for work with “select carcinogens,” reproductive toxins, or substances that have a high degree of acute toxicity.

desorption

The process of regenerating an activated carbon bed by removing contaminants.

desuperheater

A device that sprays water into steam flowing through a superheater, reheater, or line to control steam temperature; also called a spray attemperator.

desuperheating section

A baffled section inside the shell of a closed heater through which superheated extraction steam flows.

detail (A point)

Detail (A Point) To display on-screen all the information contained in a DCS relating to a specific point in a loop or process, such as configuration or alarm settings, process variable, related output devices, etc.

detail drawing

An enlarged-view drawing that shows special features of a structure more clearly.

detector

In a level measurement system that uses radiation, the part of the system that absorbs the directed beam of radiation and converts the radioactive energy into a proportional electrical current.

deterministic

If something is deterministic, you have all of the data necessary to predict (determine) the outcome with 100% certainty.

deterministic model

A deterministic model does not include elements of randomness. Every time you run the model with the same initial conditions you will get the same results.

detraining tank

A tank in a seal oil system that allows oil to stand so that trapped air or hydrogen can bubble off before the oil is reused.

developed acreage

The number of acres that are allocated or assignable to productive wells or wells capable of production.

developed reserves

Reserves that can be expected to be recovered through existing wells with existing equipment and operating methods or in which the cost of the required equipment is relatively minor compared to the cost of a new well and, if extraction is by means other than a well, through installed equipment and infrastructure operational at the time of the reserves estimate.

development phase

The phase of petroleum operations in which a proven oil or gas field is brought into production by drilling development wells and constructing surface processing and field pipeline facilities.

development well

A well drilled within the proved area of an oil or gas reservoir to the depth of a stratigraphic horizon known to be productive.

development wells

Development wells are drilled to economically drain the reservoir. Some of these wells are drilled at the outset, while others are added later in the life of the field as production begins to decline. To enhance recovery, fluids such as water, gas, carbon dioxide (CO₂), chemicals, or steam may be injected into the reservoir at a later stage.

deviation

The difference between the set point and the value of a process variable; also called error.

device function numbers table

A table that identifies the general functions of many electrical devices in terms of number designations.

DeviceNet

Allen-Bradley's proprietary network for connecting individual input and/or output devices and their power sources to a PLC system.

DeviceNet protocol

A standard communications protocol that governs the transmission of data through networks.

dew point

The temperature at which vapor condenses into a liquid. Used as a measure of water vapor or hydrocarbon content in natural gas.

dew point depression

The amount which the dew point is lowered.

Dewar flask

A Dewar flask is a glass or metal container made like a vacuum bottle.

DH+

Data Highway Plus. An Allen-Bradley peer network for connecting members of the PLC-5 family, some newer members of the SLC-500 family, PCs, and high-end HMIs together.

DH-485

Data Highway 485. An Allen-Bradley peer network for connecting members of the SLC-500 family, PCs, and low-end HMIs together.

diagenesis

The process by which sediments are lithified into sedimentary rocks through physical, chemical, and biological changes that occur during and after burial, including water-rock interactions, microbial activity, and compaction. Diagenesis transforms sediments into sedimentary rocks, altering their mineralogy, texture, and other properties.

diagenesis, diagenetic

Diagenesis is the term for the physical and chemical changes occurring during the conversion of sediment to sedimentary rock.

diagenetic

Diagenesis is the physical and chemical changes that occur when sediment is transformed into sedimentary rock, which involves processes such as mineral dissolution, precipitation, and microbial reactions.

diagram abbreviations table

A table that lists abbreviations commonly used to identify components in an electrical system.

diagrams and figures

Illustrations that appear in the NFC.

dial indicator

A precision measurement instrument that indicates values using a pointer and a scale, often in 1 mil increments, used to determine variance in the dimensions of a rotating surface and to measure very small movements, usually to the nearest 0.001 inch.

diameter

The length of a straight line passing through the center of a circle from one side to the other.

diaphragm

In a turbine, a stationary part that contains blades or nozzles to direct steam between rotating blade sets. In a valve, a flexible material that serves as the flow control component.

diaphragm pressure element

A type of pressure element that has a plate, or diaphragm, that flexes in response to changes in pressure and moves a pointer through a mechanical linkage.

diaphragm pump

A reciprocating pump that uses a flexible diaphragm to move fluid.

diaphragm valve

A valve that uses a flexible diaphragm instead of a disc to control fluid flow.

diapirism

Diapirism is the process in which buoyant and deformable material, such as salt, rises through the surrounding rocks, forming a bulbous-like structure.

dielectric constant

The ratio of the permittivity of a substance to the permittivity of free space, measuring the ability of a substance to store electrical energy in an electric field. It is the electrical equivalent of relative magnetic permeability.

dielectric log, dielectric propagation log

A dielectric log measures the high frequency (on the order of 25 MHz) dielectric properties of the formation. The log usually includes two curves: the relative dielectric permittivity, symbolized by epsilon which is unit less, and the resistivity in ohm-m.

dielectric log, dielectric propagation log, dielectric

dielectric permitivity

A physical property which characterizes the degree of electrical polarization a material experiences under the influence of an external electric field.

dielectric permittivity

The degree to which a medium resists the flow of electric charge, defined as the ratio of electric displacement to electric field strength. It characterizes the degree of electrical polarization a material experiences under an external electric field.

diethanolamine (DEA)

A type of amine that consists of one nitrogen atom, one hydrogen atom, and two ethanol molecules.

differential

A method of transmitting signal data in which the data always includes opposite states.

differential amplifier

An op amp circuit that is a combination of an inverting amplifier and a non-inverting amplifier; the output depends on the difference between the signals applied to the input terminals.

differential encoder

A type of encoder in which the transmitted signal data always includes opposite states.

differential expansion

An uneven response to temperature change that is experienced by components such as the rotor and shell of a turbine.

differential gain error

The change in ac gain with change in dc level.

differential input resistance

The small-signal resistance between two ungrounded input terminals.

differential input voltage

The voltage at the non-inverting input with respect to the inverting input.

differential phase error

The change in AC phase with change in DC level.

differential pressure

The difference between two related pressures, such as inlet and outlet pressures in a heat exchanger, or upstream and downstream static pressures in a pipe. Often measured in inches of water. In reciprocating compressors, it operates the suction and discharge valves.

differential pressure (D/P) cell

A device used to measure the difference between two related pressures, such as an indirect level measurement device that measures the pressure difference from the bottom to the top of a tank.

differential relay

A relay that compares current going to a device with current leaving the device and trips circuit breakers to isolate a fault under undesirable conditions.

differential spectrum method

The differential spectrum method (DSM) in NMR logging is a commonly-used commonly used fluid identification method.

differential stress

Differential stress is the difference between the greatest and the least compressive stress experienced by an object.

differentiator

A circuit that develops a constant output voltage, given a changing input voltage over a period of time.

diffuser

A set of stationary vanes that surround an impeller in a centrifugal pump, directing fluid away from the impeller and converting fluid speed into pressure while minimizing radial thrust.

diffusivity

Diffusivity (D) in NMR logging is a measure of the extent to which molecules move at random in the fluid.

digital

An electronic signal that uses two discrete states (such as 1 and 0) to represent analog or varying measurements. Also refers to two-way communication between a smart field device and a controller or DCS, and to data in the form of digits or numbers.

digital circuit

A circuit that functions like a switch, in that it is either "on" or "off'; more correctly called a binary circuit.

digital data

Digital data is information represented as a string of discrete symbols each of which can take on one of only a finite number of values from some alphabet, such as letters or digits.

digital display

A display that shows numeric values; used in test instruments that employ solid-state integrated circuits.

digital logic circuit

See Logic circuit.

digital logic element

See Logic gate.

digital meter

An instrument that expresses a variable value as a series of numbers, which can either be electronically lighted or displayed on a mechanically rotated set of wheels.

digital signals

On/off signals that can be considered as a series of electrical pulses or information bits.

digitization

Digitization is the conversion of text, pictures, or well log curves into a digital form that can be processed by a computer.

digits

Figures that are used to represent numbers in a number system; the base ten number system has ten digits.

dike

A walled containment area or barrier that surrounds one or more above ground storage tanks, used to confine liquids in an enclosed space.

dilute phase

The area at the top of a regenerator where there is less concentration of catalyst and very little combustion takes place.

dilute solution

A solution that contains a relatively small amount of dissolved solute per unit volume of solution.

diode

An electrical device that allows the passage of current in one direction only; typically used to convert AC into DC.

dip

The magnitude of the inclination of a plane from the horizontal.

dipmeter

A dipmeter, sometimes termed a diplog depending on the logging service company, is a well logging instrument designed to determine the direction and angle of dip of geological formations.

dipmeter, dip

A dipmeter is a tool for measuring the formation dips in a wellbore.

dipmeter/diplog

A dipmeter (sometimes termed a diplog depending on the logging service company) is a well logging instrument designed for determining the direction and angle of dip of geological formations.

dipole sonic logging tool

A diploe sonic logging tool is a sonic array tool in which sources are dipoles, as opposed to radially symmetric monopoles, so that it generates both P- and S-waves in formations.

dipstick

A calibrated rod specifically designed to read liquid levels on a particular engine or piece of machinery. When a dipstick is inserted into and withdrawn from a liquid, the level is the point at which the liquid no longer coats the rod.

dipswitches

Small on/off switches that are frequently used for configuring PLCs.

direct acting

A controller setup in which an increase in the value of the input causes an increase in the value of the output.

direct current

Current that flows in only one direction.

direct current (DC)

Current that flows in only one direction.

direct hydrocarbon indicator (DHI)

A direct hydrocarbon indicator (DHI), is any seismic attribute that indicates the presence of hydrocarbons. DHIs are particularly useful in hydrocarbon exploration for reducing the risk of exploration wells. DHIs most commonly occur as bright spots, a local high amplitude anomaly which are displayed with bright colors so as to stand out from background amplitude variation, or as flat spots, which are horizontal reflectors that cross existing stratigraphy and indicate a hydrocarbon fluid level within an oil or gas reservoir.

direct level measurement device

A device that indicates level based on the distance between the surface of the substance being measured and some reference point.

directional drilling

The application of special tools and techniques to drill a wellbore at a predetermined angle. Horizontal drilling is a form of directional drilling where the wellbore is ultimately drilled at +/- 90 degrees to the vertical direction.

directional overcurrent relay

An overcurrent relay unit and a directional relay unit combined in a single case.

directional unit

Part of a directional overcurrent relay that operates when current flow is in an undesirable direction.

disaggregated sample

A disaggregated sample is one that is no longer held together by cement.

disbonding of coating

The failure of a coating to adhere to the substrate to which it was applied. It is a loss of adhesion between a cathodic coating and its metal substrate due to a cathodic reduction reaction (corrosion reaction) taking place.

disc

A movable part of a valve that presses against a seat to stop fluid flow. In safety valves, it is the part that blocks the path between the inlet and outlet.

discharge pressure

The pressure at the discharge port of a compressor.

discharge ring

A component of a multistage centrifugal pump that mounts onto the shaft and prevents leakage between two stages; may also be called a stage piece.

discharge valves

Valves which open to discharge compressed gas.

disconformity

A disconformity is an unconformity between parallel layers of sedimentary rocks which represents a period of erosion or non-deposition.

disconnect device

A device capable of breaking the electrical connection between a motor branch circuit and a power source.

discovery

A petroleum accumulation for which one or more exploration wells have established the existence of a significant quantity of potentially moveable hydrocarbons.

discrete

Discrete In process control, generally a reference to output devices, such as valves or pumps, that are used in only two possible states: on or off, open or closed, etc.

discrete (bit) module

A type of I/O module that handles an individual input or output device on each of its terminals.

discrete component

A component that functions individually in a circuit.

discrete device

A device that switches between only two states: on and off, closed and open, etc.

discrete fracture network (DFN)

A discrete fracture network (DFN) refers to a computational model that explicitly represents the geometrical properties of each individual fracture (e.g., orientation, size, position, shape and aperture), and the topological relationships between individual fractures and fracture sets.

discussion [evidence]

Discussion enables a holistic approach to assessment that can test the validity and reliability of other evidence. In order to be successful, it must be well planned. Considerations during the planning for this type of method include:

What is purpose?
What is required outcome?
Does it meet evidence requirement, or fill gaps?

dish structures

Dishes are a type of sedimentary structure formed by liquefaction and fluidization of water-charged soft sediment either during or immediately following deposition. These structures are most commonly found in turbidites and other types of clastic deposits that result from subaqueous sediment gravity flows.

dispersed contact leaching

A type of leaching system that removes a soluble component from solid particles that are suspended in the solvent; both the particles and the sol vent are in motion during the time of contact.

dispersion

In physics, dispersion describes the effect on the properties of a wave traveling through a medium. In statistics, a term describing the size of the distribution of values expected for a particular variable, measurable by range, variance, and standard deviation.

displacer

A level measurement device that operates on the principle of buoyancy—a cylinder or sphere suspended in a liquid whose apparent weight changes are proportional to changes in level. Also, a piston or sphere that displaces a fixed volume of fluid in a pipe prover.

dissipate

Dissipation embodies the concept of a dynamical system where important mechanical models, such as waves or oscillations, lose energy over time, typically from friction or turbulence. The lost energy converts into heat, which raises the temperature of the system. Such systems are called dissipative systems.

dissolved gases

Gases in solution in cooling water that can produce or speed up corrosion, which deteriorates metal in pipes and equipment.

dissolved solids

Contaminants, such as calcium and magnesium, in water that can cause scale buildup.

distance piece

The housing which connects the compression unit to the drive unit.

distance relay

A relay that operates in response to a specific ratio of voltage to current on a protected transmission line.

distillate

The liquid that is condensed from process vapours other than steam.

distillate fuels

Fuels, such as jet fuel, diesel fuel, and furnace oil, that are produced by blending components from the middle of the crude oil barrel.

distillation

The regeneration process of removing water from glycol, or acid gases from amine solution, by heating.

distillation process

The process of removing water from glycol by raising the temperature above the boiling point of water, or removing acid gases from amine by generating steam to strip the acid gases.

distillation system

A group of equipment designed to separate materials.

distributary mouth bar

When sediment-laden river water flows into the standing water at the mouth of a distributary, the river water slows and deposits its load. This forms a sediment body called a distributary mouth bar, or bar finger sand.

distribution

An operation in which the quantity that is outside of a grouping symbol is multiplied by each term that is inside the grouping symbol.

disulfides (RSSR)

Sulfur compounds that do not have an offensive odor.

ditch cuttings

Small pieces of rock that break away due to the action of the drill bit's teeth, which are screened out of the liquid mud system at the shale shakers.

ditch cuttings, drill cuttings

Ditch, or drill, cuttings are small pieces of rock that break away due to the action of the drill bit's teeth, which are screened out of the liquid mud system at the shale shakers.

diverter valve

A three-way valve on the LACT unit which automatically directs bad oilto the treating system or directs good oil to the meter for sales.

dividend

The number that is to be divided in a division problem.

divider bar

The line that separates the numerator and the denominator in a fraction.

divider blocks

A device used to divide oil evenly to each injection point.

division

A subcategory of a hazardous materials class.

divisions

Measurement markings on an oscilloscope graticule.

divisor

The number that does the dividing in a division problem.

DMO

DMO, or dip moveout, is a processing correction for the effect of dip on stacking velocities, which preserve reflections that have differing dips during stacking.

DN

The mnemonic for the "Done" bit in many common functions. The rung becomes true when the instruction has finished.

dockman

An operator who works on a dock during a barge transfer.

document repository

The area in CMS Online where users can access procedure-related as well as other useful documents. Depending on the access privileges, users may be able to view all documents across the organization and upload new ones. Dashboard > 9-dot icon (upper right) > Resources > Documentation.

dog leg

A dog leg is a particularly crooked place in a wellbore where the trajectory of the wellbore in three-dimensional space changes rapidly.

dogleg, dog leg

A dog leg is a particularly crooked place in a wellbore where the trajectory of the wellbore in three-dimensional space changes rapidly.

dolomite

An anhydrous carbonate mineral composed of calcium magnesium carbonate.

dolomitization

A geological process by which the carbonate mineral dolomite is formed when magnesium ions replace calcium ions in calcite. This commonly occurs in sabkha areas.

double

Two joints of drill pipe (each approximately 30 ft / 9.1 m in length) screwed together.

double block and bleed

A type of fuel gas valve arrangement that automatically shuts off fuel flow and diverts trapped fuel to collection or disposal equipment.

double insulated tool

An electrical tool that has a plastic casing designed to insulate the user from any fault inside the tool.

double-acting compressor

A compressor which compresses gas on both the forward and backstrokes.

double-acting piston pump

A piston pump that both admits and discharges liquid on each part of the reciprocating movement.

double-acting pump

A reciprocating pump that admits and discharges fluid on each part of the reciprocating movement.

double-action lock

A lock that requires at least two separate, consecutive actions to open it.

double-arm mixer

A mixer that has two mix blades, each of which is mounted on a shaft.

double-cone dryer

A type of rotary dryer that is shaped like two cones that are connected.

double-duct ventilation system

A system characterized by a supply air duct that branches into two supply air ducts (one for heating and one for cooling), and a return air duct.

double-suction impeller

An impeller that has a suction eye on each side.

dowel pins

Pins that are used to help align parts of a pump, such as a bearing housing or the two halves of the casing.

down time

The time during which a machine or process has been idle, or otherwise not producing.

downcomers

In drum-type boilers, the large pipes that recirculate water from the steam drum back to the waterwalls. In separators, vertical piping that allows liquids to flow from the top tube to the bottom tube of a two-tube horizontal separator.

download

Allen-Bradley's term for copying a PLC project from a PC to a PLC.

downloading

The process of electronically transferring data or files from one device to another, such as from a programming terminal (PC) to a PLC, or from an EFC to a handheld device or central control station.

downstream

A term used for anything located past the orifice plate or metering device in a meter tube in the direction of flow.

downstroke

The downward movement of the sucker rod string.

downthrown fault block

In a downthrown fault block, the hanging wall has moved downwards relative to the footwall. This usually occurs with normal faulting, which occurs when the crust is extended. Alternatively, such a fault can be called an extensional fault.

draft

The flow of air and other gases through a boiler or furnace, typically indicated by pressure instruments.

drag with faulting

Fault drag refers to the deflection of curved markers adjacent to a fault.

drain cooler

A section inside the shell of a closed heater that surrounds the tube bundle near the heater's inlet water box. Drips collect there and are subcooled to keep them from flashing to steam in the drain line.

drain cooler approach (DCA)

The difference between the temperature of the drips leaving the drain cooler of a closed heater and the temperature of the condensate or feedwater entering the tubes from the inlet water box.

drain pad

An area at a loading site through which spills drain to a collection point for recovery and treatment or disposal.

drainage

Drainage is the process of forcing a non-wetting phase into a porous rock.

drainage area of a well

Drainage area of a well is the reservoir area or volume drained by the well. When several wells drain the same reservoir, each drains its own drainage area, a subset of the reservoir area.

draw

A product that flows out of a multidraw tower.

draw temperature

The temperature at which a side-stream is drawn from a distillation tower.

draw works

The machinery on a drilling rig consisting of a large diameter steel spool, brakes, a power source, and various auxiliary devices. Its primary function is to reel out and reel in the drilling line (a large-diameter wire rope) in a controlled manner.

drawdown well test

A drawdown well test is one in which the flow rate is held approximately constant while the well pressure is measured.

drawdown, pressure drawdown

Pressure drawdown is the difference between the reservoir pressure and the flowing wellbore pressure, which drives fluids from the reservoir into the wellbore.

drift pin

A metal tool with a pointed end used to align adjoining components, i.e., bolt holes of valves and flanges or a pair of mating flanges.

drill bit

A piece of equipment that cuts or crushes formation rock, attached to a drill string where forces are applied to rotate it. Also, the replaceable cutting attachment used in a power drill.

drill collar

A component of a drill string that provides weight on bit for drilling. Drill collars are thick-walled tubular pieces machined from solid bars of steel, usually plain carbon steel but sometimes nonmagnetic nickel-copper alloy or other nonmagnetic premium alloys.

drill cuttings

Small pieces of rock chipped away by a drill bit while drilling a well, which are transported to the surface by drilling mud and screened out of the liquid mud system at the shale shakers. Also called rock cuttings or simply cuttings.

drill cuttings, ditch cuttings

Drill, or ditch, cuttings are small pieces of rock that break away due to the action of the drill bit's teeth, which are screened out of the liquid mud system at the shale shakers.

drill pipe

A tubular steel conduit fitted with special threaded ends called tool joints. The drill pipe connects the rig surface equipment with the bottom hole assembly and the bit.

drill stem test

A procedure for isolating and testing the pressure, permeability, and productive capacity of a geological formation in situ within a reservoir during the drilling of a well. The zone is sealed off from the rest of the wellbore by packers, and the formation's pressure and fluids are measured.

drill string

The drill string, also called the drillstem, is the combination of the drill pipe, the bottomhole assembly (BHA), and any other tools used to make the drill bit turn at the bottom of the borehole.

drill-off trend

Drill-off trend is a gradual and uniform increase in the ROP, typically associated with increasing formation pressure.

drilling break

A drilling break is a sudden increase in the rate of penetration during drilling.

drilling fluid

Drilling fluid, also called drilling mud, is a specially formulated mixture of solids, liquids, and/or gases used when drilling an oil well. The formulation of the mud depends on several factors, for example, the type of formation being drilled. The main purposes of drilling fluid include cooling the drill bit, removing the cuttings from under the bit and circulating them to the surface, and well control during drilling.

drilling line

A drilling line is a wire rope hoisting line, reeved on the sheeves of the crown block.

drilling mud

Mixtures of fluids and solids (as solid suspensions, mixtures, and emulsions of liquids, gases, and solids) used in well operations to drill boreholes.

drilling mud filtrate

Drilling mud filtrate is the liquid that passes through a filter cake from a slurry held against the filter medium, driven by differential pressure. Dynamic, or static, filtration can produce a filtrate.

drilling mud pulse telemetry

The most common method used for data transmission in MWD and LWD systems. The three main systems are positive pulse, negative pulse, and continuous wave, named for the ways their pulses are propagated in the mud volume.

drilling mud slowness

Drilling mud slowness is the travel time per foot, termed DTmud, traveled by the acoustic wave in the drilling mud.

drilling mud, mud

Mixtures of fluids and solids (as solid suspensions, mixtures, and emulsions of liquids, gases, and solids) used in well operations to drill boreholes.

drilling mud, mud, drilling fluid

Drilling muds are mixtures of fluids and solids (as solid suspensions, mixtures and emulsions of liquids, gases and solids) used in well operations to drill boreholes.

drilling overbalanced

Drilling overbalance conditions occur when the hydrostatic pressure in the wellbore is greater than the reservoir pressure.

drilling rig

The machine used to drill a wellbore.

drips

Condensate that forms on the shell side in a closed heater as steam transfers its heat to the condensate or feedwater.

drive

Generally, a combination of a motor, its controller, and other associated control or field devices.

drive sleeve

A component of a motor operator that transmits the motion of the worm gear to the valve stem.

drive unit

The power source for a compressor which is either an electric motor or engine.

driver

A computer program that allows a non-standard hardware device or network to communicate with a PC system. Also, a source of power such as an electric motor, engine, or steam turbine.

driving potentials

The difference in potential between the anode and the cathode. The output current of the anodic material depends on the driving potential and the resistance between the anode and the structure to be protected (cathode).

drop-out voltage

The amount of voltage needed to reposition a relay element.

drum

A round switch that opens or closes electrical contacts by rotating. Also called a rotor.

drum dryer

A dryer that uses one or more heated drums to dry a wet cake that is very dilute, in a slurry-like form.

drum filter

A device that uses a rotating screen and a vacuum to remove solid particles from water.

drum, logging drum

A drum is used for spooling the wireline cable when it is not down the borehole.

drum-type boiler

A type of boiler that has a large steam drum located on top to collect the steam produced by the boiler.

dry formation test

A dry formation test is one that does not acquire a valid formation pressure.

dry gas

Dry gas is almost pure methane and occurs in the absence of liquid hydrocarbons or by processing natural gas to remove liquid hydrocarbons and impurities.

dry gas / lean gas

A gas made up of primarily light hydrocarbon vapors.

dry glycol (or lean glycol)

Glycol that is free of water.

dry hole

A well found to be incapable of producing either oil or gas in sufficient quantities to justify commercial exploitation or completion.

dry ice

The solid form of carbon dioxide.

dry trays

An abnormal condition that occurs in a distillation tower when there is not enough liquid on the trays.

dry-type filter

A filter made of a dry filter material that is held in a frame; may be stationary or movable.

drying

The process of removing liquid from a solid or a gas, by either heat transfer or the use of an adsorbent.

DSM

differential spectrum method.

dual porosity reservoir

A reservoir characterized by having primary porosity from original deposition and secondary porosity from diagenesis or other mechanisms, in which all flow to the well effectively occurs in one porosity system and most of the fluid is stored in the other. Examples include naturally fractured reservoirs, vugular carbonates, and layered reservoirs with extreme permeability contrasts.

dual water interpretation model

The dual water interpretation model is a petrophysical interpretation model of shaly formations that considers there to be two different waters in the pore spaces: far water, which is the normal formation water; and near water, or clay-bound water, in the electrical double layer near the clay surface.

dual water model

The dual water model is a model of shaly formations that considers there to be two waters within the pore spaces: far water, which is the normal formation water; and near water, or clay bound water, in the electrical double layer near the clay surface. The clay bound water consists of clay counterions and the associated water of hydration.