| Decentralisation |
To eccenter. To purposely force a tool against the borehole or casing wall by means of an arm or bow spring. |
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| DECT |
Downhole Electric Cutting Tool |
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| Deformation |
A term, usually applied to completion tubulars which are distorted. |
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| Density |
Mass per unit volume (often expressed as specific gravity). Well-logging units are g/cm3, often written g/cc. |
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| 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. |
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| Depth Encoder (ENC) |
A device which detects depth measurements and converts them to electrical signals for input into data acquisition systems. |
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| Depth Interface Unit (DIU) |
USB device interfacing a depth encoder, analogue and digital inputs to a logging system. |
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| Depth Offset |
Any difference in depth between a reference and another point in the well. Usually applied to sensor offsets in a toolstring. |
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| 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. |
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| Derrick |
The tower-like structure that houses most of the drilling controls. |
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| Development phase |
The phase in which a proven oil or gas field is brought into production by drilling production (development) wells. |
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| Deviation |
Angle of the well or toolstring away from vertical. |
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| Differential Pressure |
The rate at which pressure is changing down the well. (psi/ft or bar/m). |
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| Diverter Basket Flowmeter (DBT) |
A flowmeter with an opening basket below the spinner, which forces all the fluids to flow through it. |
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| Downlink |
Commands and/or data sent downhole via the Sondex Ultralink cable telemetry system. |
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| 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. |
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| 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. |
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| 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. |
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| Dry hole |
A well which has proved to be non-productive. |
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| Dummy Logging Cable (DLC) |
A dummay cable used in situations where a real logging cable is unavailable or impractical.
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