Page 495 - Practical Well Planning and Drilling Manual

Appendix NEW! revised 11/00/bc 1/30/01 3:30 PM Page 471

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Glossary

Darcy. A unit of permeability. A porous medium has a permeability
of 1 darcy when a pressure of 1 bar on a sample 1 cm long and 1 sq
cm in cross section will force a liquid of 1 centipoise viscosity
through the sample at the rate of 1 cc per sec.

Dead Line or Deadline. Refers to the end of the drilling line which is
not reeled on the hoisting drum of the rotary rig. This end of the
drilling line is usually anchored to the derrick substructure and does
not move as the traveling block is hoisted, hence the term dead line.

Dead Man. A buried anchor to which guy-wires are tied to steady the
derrick, boiler stacks, etc.

Deep Propagation Tool. Schlumberger wireline tool that measures the
signal level and relative phase of a 25 MHz electromagnetic wave.
Used for measuring resistivity of noninvaded virgin formations, inva-
sion profiling, water saturation and lithology analysis.

Deflocculation. Breakup of flocs of gel structures by use of a thinner.

Dehydration. Removal of free or combined water from a compound.

Density. Matter measured as mass per unit volume expressed in
pounds per gallon (ppg), pounds per square inch per 1,000 ft. of
depth (psi/1,000 ft), and pounds per cubic ft (lb/cu ft). Density is
commonly associated with “mud weight”. Mud densities should
properly be expressed in psi/ft of hydrostatic pressure but is still com-
monly expressed as pounds per gallon.

Differential Pressure. The difference in pressure between the hydro-
static head of the drilling-fluid column and the formation pressure at
any given depth in the hole. It can be positive, zero, or negative with
respect to the hydrostatic head.

Differential-Pressure (Wall) Sticking. Sticking which occurs because
part of the drill string (often the drill collars) becomes embedded in
the filter cake resulting in a non-uniform distribution of pressure
around the circumference of the pipe. The conditions essential for

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