Page 496 - Practical Well Planning and Drilling Manual
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Appendix NEW! revised 11/00/bc 1/30/01 3:30 PM Page 472
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Glossary
sticking require a permeable formation, a pressure overbalance across
a nearly impermeable filter cake and a stationary drill string.
Dipole Shear Sonic Imager tool. Schlumberger wireline tool that
records shear, compressional and Stoneley waveforms. Used for
amplitude variation with offset (AVO) calibration, shear seismic cor-
relation, wellbore stability measurements, sanding analysis, fracture
height estimation, and sand mobility.
Dispersant. Any chemical which promotes dispersion of the dis-
persed phase.
Dispersed Phase. The scattered phase (solid, liquid, or gas) of a dis-
persion. The particles are finely divided and completely surrounded
by the continuous phase.
Dispersion (Of Aggregates). Subdivision of aggregates. Dispersion
increases the specific surface of the particle; hence results in an
increase in viscosity and gel strength.
Distillation. Process of first vaporizing a liquid and then condensing
the vapor into a liquid (the distillant), leaving behind non-volatile
substances, the total solids of a drilling fluid. The distillant is the
water and/or oil content of a fluid.
Divalent. Having a valency of two. When a salt is referred to as diva-
lent, the metal ion has a valency of two.
Dogleg. The “elbow” caused by a sharp change of direction in the
wellbore.
Dogleg Severity. A measure of how quickly the wellbore changes
direction, expressed in degrees (of total course change) per 100’ or
30m of wellbore length.
Dope. A generic term applied to all types of thread lubricants. For
casing, tubing and line pipe use lubricants specified in API Bulletin
5A. For tool joints and drill collars less than 7 inches OD, use a
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