Technical
Thesaurus oil & gas
D
Daily peak
The maximum volume of gas
delivered in anyone day during a given period, usually a calendar year.
Dangerous area
Definition of an area so
far as danger may arise from electrical causes.
Dangerous atmosphere
An atmosphere containing
any flammable gases or vapour in a concentration capable of ignition by any
cause. or containing a toxic gas or vapour in such a concentration which will
be dangerous to human life.
Darcy
A unit of permeability. A
porous medium has a permeability of I darcy when a pressure gradient of I
atm/cm on a rock sample of 1 cm2 cross section will force a liquid of 1-cp
viscosity through the sample at the rate of I cc per sec.
Data
General term used to denote
facts. numbers. letters, and symbols. The basic elements of information;
usually but not always expressed in numerical form.
Data bank
A system for describing.
storing, and retrieving high volumes of complex structured data. A data bank is
comprised of the data base and a set of data bank software (data base
management system. DBMS) which store and retrieve information according to
predefined data descriptions. and for carrying out additional operations. Also
called data base system.
Data base
Physical storage of data
belonging to a data bank.
Data processing
Any operation carried out
with data.
Data set
A logical entity of data
consisting of several elements (fields) grouped under one criterion.
Datum
Any numerical or
geometrical quantity or set of such quantities which may serve as a reference
or base for other quantities. In geodesy two types of datums must be
considered: a horizontal datum which forms the basis for computations of
horizontal control surveys in which the curvature of the earth is considered,
and a vertical datum to which elevations are referred. World Geodetic System
1972 (WGS72). Represents pre 1972 data evaluation of the best global fit datum.
Used for Transit and early GPS. World Geodetic System 1984 (WGS84). Represents
pre 1984 data evaluation of the best global fit datum. Used for transit and
LPS. Mean Sea Level (MSL). The average height of the surface of the sea at a
tide station for all stages of the tide over a given period,usually determined
from hourly height readings measured from a fixed predetermined reference level
(ChartDatum). Lowest Astronomical Tide (LAT). The lowest tide level which can
be predicted to occur under average meteorological conditions and under any
combination of astronomical conditions.
Datum (tidal)
A level of the sea defined
by some phase of the tide, from which water depths and heights of tide are
reckoned.
Datum chart
A permanently established
surface from which soundings or tide heights are referenced, usually low water.
Also called datum, datum level, datum plane, hydrographic datum, reference
level, reference plan. See datum (tidal).
Datum(geodetic)
A reference surface
consisting of five quantities: the latitude and longitude of an initial point,
the azimuth of a line from this point, and the parameters of the reference
spheroid. It forms the basis for the computation of horizontal control surveys
in which the curvature of the Earth is considered. See horizontal control
datum.
Datum(sounding)
The horizontal plane or
tidal datum to which the soundings on a hydrographic survey are reduced. Also
called datum for sounding reduction.
Daylight tour
The shift of duty on a
drilling rig that starts at or about daylight; also called morning tour. See
evening tour and graveyard tour.
Dead freight
Freight rate which is paid
on empty space in the vessel when the, charterer is responsible for the freight
rate of a full cargo. It should be paid before sailing.
Dead oil
Crude oil containing no
dissolved gas. Compare live oil.
Dead well
A well that will not flow,
and in order to produce must be kicked off or put on artificial lift.
Deadline
Refers to the end of the
hoisting line which is not reeled on the hoisting drum of the rig. This end of
the line is usually anchored to the derrick or mast substructure and does not move
as the travelling block is hoisted, hence the term deadline. Compare fast line.
Deadline tie-down anchor
A device to which the
deadline is attached, securely fastened to the mast or derrick substructure.
Also called a deadline anchor.
Deadman
Deadman control
A device for shutting down
an operation should the attendant or operator become incapacitated. The
attendant using such a device must consciously exert pressure on a hold-down
handle or lever to work the job. When pressure is relaxed owing to some
emergency, the operation will automatically come to a halt.
Deadweight tonnage (D.W.T.)
This is the actual number
of tons of cargo, bunkers, stores, etc., that can be put on board a ship to
bring her down to her marks.
Deadweight tons
Total carrying capacity of
a ship in tons when loaded to appropriate freeboard during the summer season.
Deadwood
Material inside a tank or
other vessel such as pipes, supports, and construction members that reduce the
true volume of the tank.
Deaerator
A piece of equipment
designed to remove dissolved oxygen and carbon dioxide from boiler fed water in
order to reduce corrosion in the boiler system.
Debt
A sum of money owed by one
person or organisation to another and repayable within a fixed period of time.
Decantation
Separation of a solid from
a liquid, or a liquid from a solid, by sucking, pumping or pouring the liquid
away without disturbing the solid or liquid which has settled below.
Decomposition
The breaking up of a
chemical compound to form two or more simpler molecules.
Decompression chamber
A special chamber in which
a diver gradually returns to normal conditions after working at high pressure
underwater.
Defoamer or defoaming agent
Any substance used to
prevent, reduce or eliminate foam by reducing the surface tension.
Degasser
The equipment used to
remove unwanted gas from a liquid, especially from drilling fluid.
Degassing drilling mud
An important part of
well-drilling operations is keeping the drilling mud free of entrained gas,
bubbles that enter the mud as it circulates downhole through gaseous
formations. One of three functions of mud is to provide sufficient hydrostatic
head to control a kick when high pressure oil or gas is encountered. When mud
of a certain density is circulated, it can become infused with gas to an extent
that, although the volume of mud may increase, the density is severely reduced.
To guard against this dangerous situation, the mud is degassed at the surface.
Several kinds of equipment get the gas out, but all have one aim in common; to
make it possible for the gas bubbles to free themselves. One method flows the
mud over wide sheets so the slurry is no more than one-eighth to three-eighths
thick so the bubbles may come to the surface and escape. Another method sprays
the mud against a baffle in a spray tank that squeezes out the gas. A third
method directs the mud through a vacuum tank where, under reduced atmospheric
pressure, the bubbles of gas expand and break out of the slurry.
Degree day
A measure of the extent to
which the mean daily temperature falls below an assumed base, say
Dehydration
The elimination or removal
of water which is chemically combined with a substance.
Delocalised electrons
Electrons that are not
associated with a particular atom or bond in a molecule, as in aromatic
compounds such as benzene.
Demobilisation
End of survey work or other
work period, return to port; often involving removal of hardware equipment or
personnel; the contractual time for the project (mobilisation).
Demulsifier
A chemical used to
"break down" crude oil/water emulsions. The chemical reduces the
surface tension of the film of oil surrounding the droplets of water.
Demurrage
The sum agreed by charter
to be paid as damage for delay beyond the stipulated time for loading or
discharging.
Density
A physical property of a
material defined as the weight of unit volume at a certain temperature.
Density log
A well log which records
the formation density. The tool consists of a gamma-ray source and one or more
gamma-ray detectors. Gamma-rays are back-scattered from the formation due to
Density of soundings
Intervals between lines of
sounding and soundings in the same line. Density of soundings mostly depends on
the scale and nature of the survey. Also called frequency of soundings.
De-oiling
The removal of oil
particles from water in order to produce clean effluent water.
Depletion control
A restriction imposed on
the rate at which oil and gas reserves can be depleted, i.e. from the
reservoir.
Depletion rate
The rate at which an oil
field is exhausted.
Depletion type reservoir
A reservoir from which the
oil (or gas) is produced by expansion of the fluid, rather than an influx of
water or expansion of a gas cap. Oil recovery by reservoir depletion is low,
commonly between five per cent and 20 per cent of the oil in place. Gas
recovery is high, 70-80 per cent
Deployment
Putting underwater
equipment over the stern or side or moon pool of survey ship; start work;
duration may be prescribed by specification.
Depositional environment
The conditions under which
a series of rock strata were laid down. Depositional environments are divided
into five groups: marine (ocean- borne), aeolian (wind-borne), alluvial (river
borne), deltaic (borne by a river at its delta), and interdeltaic (between
river deltas).
Depreciation
The reduction in the value
of plant or equipment over time due to wear, tear and obsolescence.
Depth ( charted)
The vertical distance from
the chart datum to the bottom.
Depth differences
The differences in depth
which may be encountered in hydrographic surveys at crossing of cross lines and
principal lines of soundings.
Derived fuel (energy)
A fuel (or form of energy)
which is produced from a basic fuel such as coal (e.g. electricity, coke or
town gas).
Derrick
The elongated pyramid of
latticed steel mounted over the bore hole for drilling and well servicing
purposes.
Derrick (production)
A steel structure built
over a production well for raising and lowering production equipment and to
provide space and support for stacking tubing and hanging sucker rods when out
of the hole.
Derrick barges
Large barges having a crane
used for lifting heavy equipment on to or off an offshore platform.
Derrick floor
A raised dais at the base
of the derrick carrying the drilling table; Sometimes called the drilling or
rig floor.
Derrick man
The member of the drilling
crew who works up the derrick; also known as the derrick monkey.
Derv / derv fuel
An acronym for diesel engine
road vehicle fuel; a medium-Iight liquid fuel derived from gas oil.
Desalting
The removal of inorganic
chloride-type impurities from crude oils.
Desanders
See hydrocyclones.
Desiccation (drying)
The removal of moisture or
the prevention of moisture pick-up from the surrounding atmosphere.
Desilters
See hydrocyclones.
Desulphurisation
Process for the removal of
sulphur and its compounds from crude oil or refined products.
Detergent
A cleansing liquid or
solid.
Deterioration
Any undesirable chemical or
physical change.
Development phase
The phase in which a proven
oil or gas field is brought into production by drilling production wells.
Development well
A well drilled with a view
to producing oil or gas from a proven field.
Deviated well
A well drilled in such a
way that its controlled direction departs progressively from the vertical; such
wells are drilled in order to reach different parts of a reservoir from a
single platform. A well may also be deviated to avoid junk drilling equipment
left in the original hole.
Deviated well
A well drilled in such a
way that its controlled direction departs progressively from the vertical; such
wells are drilled in order to reach different parts of a reservoir from a
single platform. A well maly also be deviated to avoid junked drilling
equipment left in the original hole.
Deviation
The inclination of the well
bore from the vertical. The angle of deviation, angle of drift, or drift angle
is the angle in degrees that shows the variation from the vertical as revealed
by a deviation survey. See deviation survey.
Deviation (magnet)
The angle between the
compass needle and the magnet meridian, expressed in degrees east or west of
magnetic meridian. Also called deviation.
Deviation drilling
See directional drilling.
Deviation survey
An operation made to
determine the angle from which a bit has deviated from the vertical during
drilling. There are two basic deviation surveys, or drift survey, instruments:
one reveals the angle of deviation only; the other indicates both the angle and
direction of deviation.
Dew point
The temperature at which
air is saturated with water.
DGPS
Differential GPS usage mode
involving comparison of mobile receiver and stationary reference receiver, it
allows GPS to obtain the high accuracies required for survey. See differential
GPS.
Dialkene
An aliphatic compound
containing two double carbon-to-carbon bonds in its molecule.
Diamond bit
A drilling bit that has a
steel body surfaced with industrial diamonds. Cutting is performed by the
rotation of the very hard diamonds over the rock surface.
Diesel electric power
The power supplied to a
drilling rig by diesel engines driving electric generators, used widely
offshore and gaining popularity onshore.
Diesel engines
A high-compression,
internal-combustion engine used extensively for powering drilling rigs. In a
diesel engine, air is drawn into the cylinders and compressed to very high
pressures; ignition occurs as fuel is injected into the compressed and heated
air. Combustion takes place within the cylinder above the piston, and expansion
of the combustion products imparts power to the piston.
Diesel fuel
The light oil fuel that is
used in diesel and other compression-ignition engines.
Diesel index
An index of the ignition
quality of diesel fuel obtained by calculation of the specific gravity and the
aniline point of a middle distillate fuel.
Differential GPS
Differential GPS is
implemented by placing a GPS monitor receiver at a precisely known location.
Instead of computing a navigation fix, the monitor determines the range error
to every GPS satellite it can track. These ranging errors are then transmitted
to local users where they are applied as corrections before computing the
navigation result.
Digital
Technique of representing a
sensor's input as numeric data stream (after conversion from analogue input
signal), e.g. all marine seismic including high resolution relies on
multichannel digital techniques (as opposed to analogue).
Digitise
To convert analogue data
(or physical image) to digital data, e.g. echo sounder data digitised for
logging, sonar data digitised for video output.
Dilute
To reduce the strength of
concentration of a solution by the addition of another liquid.
Diolefin
See dialkene.
Dip
A measure of the
inclination of rock strata with respect to the horizontal.
Dipping
Measurement of the depth of
liquid in a storage tank by the use of a graduated steel tape or rod.
Directional drilling
A technique whereby a well
is deliberately deviated from the vertical in order to reach a particular part
of a reservoir. See deviated well, whip stock.
Discovery well
The first oil or gas well
drilled in a new field; the well that reveals the presence of a petroleum
bearing reservoir. Subsequent wells are development wells. Compare development
well.
Dispersant
A chemical used to reduce
the surface tension between two liquids, e.g. break up an oil slick.
Dispersed phase
The scattered phase (solid,
liquid, or gas) of a dispersion. The particles are finely divided and
completely surrounded by the continuous phase.
Dispersoid
A colloid or finely divided
substance.
Displacement fluids
In oil well cementing, the
fluid, usually drilling mud or salt water, that is pumped into the well after
the cement to force the cement out of the casing and into the annulus.
Disposal well
A well used for the
disposal of (usually) salt water. The water is pumped into a subsurface
formation sealed off from other formations by impervious strata of rock; a
service well.
Dissolved gas
Gas contained in solution
with the crude oil in the reservoir.
Dissolved gas drive
The force of expanding gas
dissolved in the crude oil in the formation that drives the oil to the well
bore.
Dissolved solids
The different anions and
cations dissolved in formation waters.
Distillates
The products obtained by
condensation during the fractional distillation process, i.e. the gaseous
fuels, kerosene and gas oils.
Distillation
The process by which
liquids are separated or purified by successive vapourisation and condensation.
Diver
Anyone who works underwater
in a wet suit, diving bell or hyperbaric chamber.
Diverter
An inflatable torus which,
when pressurised, seals off the annulus causing the drilling mud to be diverted
to the mud pits on a drilling platform.
Dividend
The profit from a company
paid to its investors.
Diving bell
A pressure chamber from
which divers work underwater, the water being kept out by means of high
internal air pressure; can also be used as an observation chamber.
DMT
Acoustic Dual Mode
Transponder made by Sonardyne.
Doghouse
A smaller shelter located
on the rig floor for use by the drilling crew.
Dogleg
An abrupt change in the
direction of a well bore.
Dolomite
A rock composed of the
double carbonate of calcium and magnesium; a common reservoir material.
Doodlebugger
A member of a seismic crew.
DOP
Dilution of Precision. A
parameter relating the precision of the position (and/or an unknown auxiliary)
provided by a positioning system to that of the "observed quantities"
directly measured by the system. DOP is a measure of the influence of the
geometry of loci on the precision of position fixing. OOP is frequently used
with a qualifying term such as geometric (GOOP), horizontal (HOOP), vertical
(VOOP), etc. to indicate that OOP is related to all or some unknown quantities.
Dope
A lubricant for threads on
pipes.
Double
Two sections of drill pipe,
casing or tubing joined together.
Double block and bleed
A valving arrangement which
ensures no flow in a line, even though the valves may leak. It consists of two
block valves in the main line, with a small bleeder valve draining the line
between the block valves.
Double board
The name used for the
working platform of the derrick man or monkeyboard, when it is located at a
height in the derrick or mast equal to two lengths of pipe joined together.
Compare fourble board and thribble board. See monkeyboard.
Down dip
A term used where one well
is below another well due to inclination of the strata in which the reservoir
lies.
Down time
Time during which no
drilling or production is possible due to adverse weather conditions, while
downhole equipment is being changed, during well logging, during mechanical
breakdown etc.
Downcomer
A duct which carries the
liquid flowing down a distillation tower from one tray to the one below it.
Downhole
In a well bore.
Downhole safety valve
A valve fitted to the
production tube of a well some distance below the sea-bed in order to permit
flow to be stopped in a emergency.
Downstream
A term referring to
industry operations beyond the producing phase of the business, i.e. refining
and marketing.
Draft or draught
The vertical distance, at
any section of a vessel from the surface of the water to the bottom of the keel.
When measured at or near the bow, it is referred to as draft forward and when
measured at or near the stern as draft aft .The mean draft is the mean of the
drafts forward and aft. These drafts are more specifically described as
displacement drafts as opposed to navigational drafts which are measured to the
lowest appendage to the hull as opposed the keel.
Drape structures
This occurs when sediments
are deposited or draped over the physical relief of older rocks. Such features
can include old fault traps or anticlines.
Drawdown
The total amount that has
been borrowed under a given loan agreement.
Draw-down
The difference between the
static formation pressure and the flowing bottom hole pressure in a well.
Drawworks
The control centre from
which the driller operates the drilling machinery.
Dresser sleeve
A slip-type collar that
connects two lengths of plain-end (threadless) pipe. This type sleeve
connection is used on small-diameter, low pressure lines.
Drift (mandrel)
A device used to check the
inside diameter of casing and tubing before it is run. See go-devil.
Drift diameter
The smallest internal
diameter of a casing or tubing that is allowed, or the limit of tolerance.
Correspondingly it is the largest diameter of tool or equipment that can pass
through it.
Drill bit
The part of the drilling
tool which actually cuts through the rock.
Drill collars
Lengths of extra-heavy
steel tubing located immediately above the drill bit in order to maintain
pressure on the bit and keep the drill string in tension.
Drill pipe:
See drill string.
Drill stem
All members in the assembly
used for drilling by the rotary method from the swivel to the bits, including
the kelly, drill pipe and tool joints, drill collars, stabilisers, and various
subsequent items. Compare drill string.
Drill stem test (DST)
A test whereby the nature
and quantity of the formation fluids in a possible oil- or gas-bearing stratum
are determined by allowing them to flow to the surface through the drill string
und(!r carefully controlled conditions.
Drill string
Lengths of steel tubing
roughly
Driller
The experienced operator
who controls the drawworks and heads the drilling crew.
Drilling block
A lease or a number of
leases of adjoining tracts of land that constitute a unit of acreage sufficient
to justify the expense of drilling a wildcat.
Drilling centre
Central reference point on
the drilling deck of a platform from which the co-ordinates of each centre
point of a drilling conductor is measured.
Drilling contractor
A company that undertakes
to provide the equipment and manpower needed to drill a well on behalf of an
operator.
Drilling crew
The team who actually work
on or above the derrick floor during drilling operations generally a driller
plus four roughnecks.
Drilling engineer
The engineer who designs
the casing and is responsible for the drilling programme for a well.
Drilling floor
See derrick floor.
Drilling fluid
Circulating fluid, one
function of which is to force cuttings out of the well bore and to the surface.
While a mixture of clay, water, and other chemical additives is the most common
drilling fluid, wells can also be drilled using air, gas, or water as the
drilling fluid. Also called circulating fluid. See mud.
Drilling foreman
The supervisor of drilling
operations on a rig; also the tool pusher or rig superintendent.
Drilling jars
A jointed section in a
string of cable tools made with slack or play between the joints. If the bit
becomes lodged in the hole, the sudden jar or impact developed by taking up the
slack in the jars aids in freeing the bit.
Drilling line
The wire rope connecting
the drawworks, crown block and travelling block that is used to raise or lower
drill pipe or casing from or into a well.
Drilling mud
A mixture of clays, water
and chemicals pumped down the drill string and up the annulus during drilling
in order to lubricate the system, carry away rock cuttings, maintain the
required pressure at the bit end, provide an aid to formation evaluation, etc.
Drilling platform
An offshore platform used
to drill exploration and development wells but lacking the processing
facilities of a production platform.
Drilling rate
The speed with which the
bit drills the formation; usually called the rate of penetration.
Drilling rig
The complete machinery and
structures needed for drilling a well.
Drilling spool
A spool with side outlets
for kill and choke lines fitted between the BOP stack and the wellhead.
Drilling table
The table on the derrick
floor whereby the drill pipe is rotated; also called the rotary table.
Drill-ship
A ship fitted with a
drilling derrick that is used to drill in waters that are too deep for a
jack-up or semi-submersible rig.
Dropcorer
Soil sampling device
lowered to sea-bed and using freefall momentum to penetrate; produced cores up
to three metres long used for soil analysis (geotechnical).
Drum
Container used for storing
and transporting chemicals.
Dry gas
Hydrocarbon gas from which
the readily liquefiable components are either naturally absent or have been
removed by separation and processing. Adefined gas containing hydrocarbon
components upto C4 only as well as inerts (e.g. H2S, hydrocarbon, nitrogen,
etc.)
Dry hole
A well drilled without
finding gas or oil in commercial quantities.
Dry natural gas
Natural gas which is low in
associated liquids; mostly methane.
Dry tree
A subsea wellhead where the
equipment is enclosed in a water-tight chamber.
Drying heights
Heights above sounding
datum, of any areas (banks, foreshores, rocks etc.) which dry at low water.
DSV
Diving support vessel.
Dual completion
A mechanical arrangement
within the well so that production can be taken separately and/or
simultaneously from two reservoirs. Often two strings of tubing are run within
one production string of casing to provide production outlets from two perforated
intervals which are separated by packers. This is often called sliding sleeve
completion.
Duplex
A method in which
telecommunication between two stations can take place in both directions
simultaneously.
Duplexer
A switching device used to
connect a transmitter and a receiver to the same antenna.
Duster
A completely dry hole; a
well that encounters neither gas nor liquid at total depth.
Dutchman
The threaded portion of a
length of pipe or nipple twisted or broken off inside a collar or other
threaded fitting. Threads thus "lost" in a fitting have to be cut out
with a chisel or cutting torch.
Dyna-driII
A downhole motor driven by
drilling fluid that imparts rotary motion to a drilling bit connected to the
tool, thus eliminating the need to turn the entire drill stem to make hole. The
Dyna-Drill, a trade name, is used in straight and directional drilling.
Dynamic positioning
The method whereby a vessel
is kept on station by computer-controlled thruster propellers rather than by
anchors.
Dynamometer
The surface, or polished
rod dynamometer is a tool which records the resultant of all forces acting
along the axis of the polished rod at any particular instant of time during one
pumping stroke of a pumping unit. This load curve is recorded with respect to
polished rod position.