Abandon	To cease work on a well which is non-productive, to plug off the well with cement plugs and salvage all recoverable equipment Also used in the context of field abandonment.
Accelerometer	Device used to measure well deviation with high accuracy by way of measuring acceleration due to gravity. Used with differential pressure density tools (eg FDD) for well deviation correction and in horizontal wells to assist in interpretation.
Acquisition (Warrior module)	The recording of data in surface readout mode using Warrior software
ACTEL	Brand name of programmable logic array used in many Sondex tools for the downhole processing of data.
Actuator	Component attached to an MIT finger to allow the finger position to be measured.
Adaptor	A short, threaded piece or coupling used to adapt parts of the logging tool that cannot otherwise be coupled together because of difference in thread size or design.
Annex B	Operator's development plan for an offshore installation. It requires government approval before it can be implemented.
Annulus	The space between the drillstring and the well wall, or between casing strings, or between the casing and the production tubing.
API unit	A unit of counting rate used for scaling gamma ray curves (see PGR tool).
Appraisal Well	A well drilled as part of an appraisal drilling programme which is carried out to determine the physical extent, reserves and likely production rate of a field.
Associated Gas	Natural gas associated with oil accumulations, which may be dissolved in the oil at reservoir conditions or may form a cap of free gas above the oil.
Attenuation	Photoelectric absorption of gamma rays for the FDR; decrease in signal strength for telemetry
Barrel	A unit of volume measurement used for petroleum and its products (7.3 barrels = 1 ton: 6.29 barrels = 1 cubic metre).
bbl	One barrel of oil; 1 barrel = 35 Imperial gallons (approx.), or 159 litres (approx.); 7.5 barrels = 1 tonne (approx.); 6.29 barrels = 1 cubic metre.
bcf	Billion cubic feet; 1 bcf = 0.83 million tonnes of oil equivalent.
bcm	Billion cubic metres (1 cubic metre = 35.31 cubic feet).
Bit	Cutting or boring element used in drilling oil and gas wells.
blow-down	Condensate and gas is produced simultaneously from the outset of production.
Blow-out	When well pressure exceeds the ability of the wellhead valves to control it. Oil and gas "blow wild" at the surface.
Blow-out preventers (BOPs)	High pressure wellhead valves, designed to shut off the uncontrolled flow of hydrocarbons.
Borehole	The hole as drilled by the drill bit.
bpd	Barrels Per Day
Bubble Point	The temperature and pressure at which part of a liquid begins to convert to gas.
Bullnose	Lowest part of the toolstring if no bottom spinner is run. For Ultrawire tools, contains a terminator circuit.
Cable	Logging cable used for carrying insulated electrical conductors for SRO logging.
Cable Head	A device mounted at the end of a cable, to provide a means of mechanical and electrical connection between the cable and the logging tool.
Cable Tension	Toolstring and cable weight measured at surface on the logging unit with a tension device, or locally at the tool head using a HTU.
Caged Fullbore Flowmeter (CFB)	A type of Sondex flowmeter, mounted at the bottom of a toolstring, providing accurate flow data over a wide cross section of the casing.
CAL3	Sondex MIT control software.
Calibration	The generation of coefficients to convert from raw tool readings to engineering units.
Caliper log	The representation of  the diameter of a borehole along its depth.  Usually achieved by measuring several locations simultaneously with a Multifinger Caliper Tool (MIT).
CalTran	Sondex software to model tubular deformity using MIT data.
Capacitance Array Tool (CAT)	Tool with 12 micro capacitance probes to measure the holdup or fraction of the well occupied by oil, gas or water.
Capacitance Water Holdup Tool (CWH)	Tool which responds to the dielectric properties of the well fluids. Principally to measure the fraction of the well fluids occupied by water.
Cased Hole	The part of the well which has casing to maintain the integrity of the well.
Casing	Metal pipe cemented into the wellbore to provide, for example, structural stability and a secure environment for downhole measurement equipment.
Casing Collar Locator (CCL)	Device which detects changes in metal volume by the disturbance of a magnetic field. Typically used for depth correlation.
Casing Inspection	Examining the casing or tubing to ascertain the condition.
Casing String	The steel tubing that lines a well after it has been drilled. It is formed from sections of steel tube screwed together.
CATView	Software for showing 3D images from horizontal wells.
Cement Bond Tool (CBT)	Typically an acoustic device to determine the quality of the bond of the cement sheath around the casing.
Central estimate	A range of exploration drilling scenarios from which the following activity levels, based on recent historical experience, are adopted as the central estimates.
Centraliser	A device which positions the logging tool in the center or near center of the well bore. aligned with the wellbore axis.
Christmas tree	The assembly of fittings and valves on the top of the casing which control the production rate of oil.
Collar	A threaded coupling device to join two pieces of pipe of the same diameter. Identified by a CCL as part of depth correlation during completions.
Commercial field	An oil and/or gas field judged to be capable of producing enough net income to make it worth developing.
Completion	The installation of permanent wellhead equipment for the production of oil and gas.
Condensate	Hydrocarbons which are in the gaseous state under reservoir conditions and which become liquid when temperature or pressure is reduced. A mixture of pentanes and higher hydrocarbons.
Coning	An effect whereby the gas-liquid ratio is distorted by withdrawal of oil at an excessive rate, resulting in unwanted water production.
Connate water	Salt water occurring with oil and gas in the reservoir.
Continuous Flowmeter Spinner (CFS)	A fixed diameter flowmeter, running on ball bearings, at the bottom of the toolstring for logging in tubing.
Continuous Flowmeter, Jewelled Bearings (CFJ)	A fixed diameter flowmeter, running on jewelled bearings, at the bottom of the toolstring for logging gas wells.
Coring	Taking rock samples from a well by means of a special tool -- a "core barrel".
Corrosion	A complex chemical or electrochemical process by which metal is destroyed through reaction with its environment, eg rust.
Countrate	The output frequency of a tool measured in counts per second.
Coupling	A threaded collar for joining two pieces of pipe, casing or tubing.
Crane barge	A large barge, capable of lifting heavy equipment onto offshore platforms. Also known as a "derrick barge".
Creaming Theory	A statistical technique which recognises that in any exploration province after an initial period in which the largest fields are found, success rates and average field sizes decline as more exploration wells are drilled and knowledge of the area matures.
Crossover	i. Device which converts from one telemetry format to another; ii. Completion item to convert from one tubing size to another.
Cubic foot	A standard unit used to measure quantity of gas (at atmospheric pressure); 1 cubic foot = 0.0283 cubic metres.
Curie	A standard measure of the rate of nuclear transformations, or disintegrations equal to that of one gram of radium. This rate is 3.70 × 1010 disintegrations per second.
Curve	In well logging, a trace representing a continuous record of some property or occurrence in the wellbore environment versus depth. One or more curves may constitute a well log.
Cuttings	Rock chippings cut from the formation by the drill bit, and brought to the surface with the mud. Used by geologists to obtain formation data
Decentralisation	To eccenter. To purposely force a tool against the borehole or casing wall by means of an arm or bow spring.
DECT	Downhole Electric Cutting Tool
Deformation	A term, usually applied to completion tubulars which are distorted.
Density	Mass per unit volume (often expressed as specific gravity). Well-logging units are g/cm3, often written g/cc.
Depth Correlation	A means of relating a log depth scale to another log or completion diagram. Sometimes applied to a separate run with, say, a GR & CCL.
Depth Encoder (ENC)	A device which detects depth measurements and converts them to electrical signals for input into data acquisition systems.
Depth Interface Unit (DIU)	USB device interfacing a depth encoder, analogue and digital inputs to a logging system.
Depth Offset	Any difference in depth between a reference and another point in the well. Usually applied to sensor offsets in a toolstring.
Depth/Time Recorder (DTR)	A battery-powered device attached to the winch encoder, for recording the time and tool depth simultaneously. Necessary for Memory Logging.
Derrick	The tower-like structure that houses most of the drilling controls.
Development phase	The phase in which a proven oil or gas field is brought into production by drilling production (development) wells.
Deviation	Angle of the well or toolstring away from vertical.
Differential Pressure	The rate at which pressure is changing down the well. (psi/ft or bar/m).
Diverter Basket Flowmeter (DBT)	A flowmeter with an opening basket below the spinner, which forces all the fluids to flow through it.
Downlink	Commands and/or data sent downhole via the Sondex Ultralink cable telemetry system.
Drift	The attitude of a borehole. The Drift Angle is the angle between the borehole axis and the vertical; the Drift Azimuth is the angle between north and the vertical projection of the borehole on a horizontal surface.
Drilling rig	A drilling unit that is not permanently fixed to the seabed, e.g. a drillship, a semi-submersible or a jack-up unit. Also means the derrick and its associated machinery.
Dry Gas	Natural gas composed mainly of methane with only minor amounts of ethane, propane and butane and little or no heavier hydrocarbons in the gasoline range.
Dry hole	A well which has proved to be non-productive.
Dummy Logging Cable (DLC)	A dummay cable used in situations where a real logging cable is unavailable or impractical.
E&A	Exploration and Appraisal.
E&P	Exploration and Production.
Eccentralisation	The degree by which a tool is displaced away from the centre of the well.
Electron Density	The parameter actually measured by the FDR, related to density by calibration and/or characterisation.
Encoder	An electrical device for measuring rotation. Fitted to a measure wheel on a winch unit to determine the amount of cable payed out.
Enhanced oil recovery	A process whereby oil is recovered other than by the natural pressure in a reservoir.
Exploration drilling	Drilling carried out to determine whether hydrocarbons are present in a particular area or structure.
Exploration phase	The phase of operations which covers the search for oil or gas by carrying out detailed geological and geophysical surveys followed up where appropriate by exploratory drilling.
Exploration well	A well drilled in an unproven area. Also known as a "wildcat well".
Farm in	When a company acquires an interest in a block by taking over all or part of the financial commitment for drilling an exploration well.
FDD	Differential Pressure principle Fluid Density Tool.
FDR	Radioactive signal attenuation principle Fluid Density Tool.
Field	A geographical area under which an oil or gas reservoir lies.
Finger	One of a number of sensors which form part of a caliper tool, for measuring casing diameter and condition across wellbore depth.
Fishing	Retrieving objects from the borehole, such as a broken drillstring, or tools.
Flowmeter	Device to measure the flowrate of the well, usually by determination of fluid velocity.
Formation	A general term applied in the well-logging industry to the external environment of the drilled well bore.
Formation pressure	The pressure at the bottom of a well when it is shut in at the wellhead.
Formation water	Salt water underlying gas and oil in the formation.
Fracturing	A method of breaking down a formation by pumping fluid at very high pressures. The objective is to increase production rates from a reservoir.
G	Gas.
G/C	Gas Condensate.
Gas field	A field containing natural gas but no oil.
Gas Holdup Tool (GHT)	A gamma ray attenuation tool to determine the gas percentage in well fluid.
Gas injection	The process whereby separated associated gas is pumped back into a reservoir for conservation purposes or to maintain the reservoir pressure.
Gas Lift	The process of raising or lifting fluid from a well by injecting gas down the well through tubing or through the tubing-casing annulus.
Gas/oil ratio	The volume of gas at atmospheric pressure produced per unit of oil produced.
GHTcalc	A software tool to calculate gas percentage from raw data from the GHT.
GO	Gearhart Owen.
Gravel pack	A slotted or perforated liner placed in the well, surrounded by small size gravel, to prevent sand flowing into the well whilst allowing continuous rapid production.
Gravel Pack Tool (GPT)	A gamma ray attenuation tool to determine the density of a gravel pack.