BAKER HUGHES - Drilling Fluids Reference Manual

GLOSSARY OF TERMS
Diatomite - A soft, silica-rich sedimentary rock comprising diatom remains that forms most
commonly in lakes and deep marine areas.
Diatomaceous Earth - An infusion earth composed of siliceous skeletons of diatoms and being very
porous. Sometimes used for combating lost circulation and as an additive to cement; also has been
added to special drilling fluids for a specific purpose of application. Also used as a filtering medium
to remove undesirable solids from clear fluids (usually brines).
Differential Pressure - The difference in pressure between the hydrostatic head of the drilling-fluid
column and the formation pressure at any given depth in the borehole. It can be positive, zero, or
negative with respect to the hydrostatic head.
Differential-Pressure (Wall) Sticking – When part of the drillstring (usually 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 sticking require a permeable formation and a
pressure differential across a nearly impermeable filter cake and drillstring.
Diffusion - The spreading, scattering, or mixing of a material (gas, liquid, or solid).
Dilatant Fluid - A dilatant or inverted plastic fluid usually made up of a high concentration of well
dispersed solids which exhibits a non- linear consistency curve passing through the origin. The
apparent viscosity increases instantaneously with increasing rate of shear. The yield point, as
determined by conventional calculations from the direct-indicating viscometer readings, is negative;
however, the true yield point is zero.
Diluent - Liquid added to dilute or thin a solution.
Direct-Indicating Viscometer - See Viscometer, Direct-Indicating.
Dispersant - Any chemical which promotes the subdivision of the dispersed phase by neutralization
of counter charges.
Dispersed Phase - The scattered phase (solid, liquid, or gas) of dispersions. 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.
Dispersoid - A colloid or finely divided substance.
BAKER HUGHES DRILLING FLUIDS
REFERENCE MANUAL
REVISION 2006 15-14