Page 310 - Shale Shakers Drilling Fluid Systems

292 SHALE SHAKERS AND DRILLING FLUID SYSTEMS

Density Density is the mass per unit volume expressed in pounds per gallon (ppg),
grams per cubic centimeter (gm/cc), and pounds per cubic ft (Ib/cu.ft).
Drilling fluid density is commonly referred to as "mud weight."

Desand To remove most API sand (>74 microns) from drilling fluid.

Desander A hydrocyclone with an inside diameter of 6 inches or larger that can
remove a high proportion of solids larger than 74 micrometer. Generally,
desanders are used on unweighted muds. See.- Cyclone, Hydrocyclone,
Hydroclone, Desilter.

Desilt To remove most silt particles greater than 15-20 microns from an unweighted
drilling fluid. The desilter is not normally used on weighted drilling flu-
ids because it can remove large amounts of barite.
Desilter A hydrocyclone with an inside diameter less than 6 inches. They can re-
move a large fraction of solids larger than 15-20 microns. See: Cyclone,
Hydrocyclone, Hydroclone, Desander.

Destabliziation A condition where colloidal particles no longer remain separate and dis-
crete, but instead contact and agglomerate with other particles.

Diatomaceous Earth A natural earth compound composed of siliceous skeletons of diatoms,
which is very porous. Sometimes used for controlling lost circulation,
seepage losses, and as an additive to cement.

Diesel Oil Plug See.- Gunk Plug.

Differential Angle Deck A screen deck in which successive screening surfaces of the same deck
are at different angles.

Differential Pressure The difference in pressure between two points. Usually, differential pres-
sure refers to the difference in pressure at a given point in the wellbore
between the hydrostatic pressure of the drilling fluid column and the
formation pressure. Differential pressure can be positive, zero, or nega-
tive with respect to the formation pressure. See.- Back Pressure.

Differential Pressure Sticking Sticking which occurs when a portion of the drill string (usually the drill
collars) becomes embedded in the filter cake resulting in a nonuniform
distribution of pressure around the circumference of the pipe. The con-
ditions essential for sticking require a permeable formation and a posi-
tive pressure (from wellbore to formation) differential across a drill string
imbedded in a poor filter cake. See: Stuck.

Differential Sticking See.- Differential Pressure Sticking.

Diffusion The spreading, scattering, or mixing of material (gas, liquid, or solid).

Dilatant Fluid Opposite of shear thinning. A dilatant or inverted plastic fluid is usually
made up of a high concentration of well-dispersed solids, which exhibit
a nonlinear consistency curve passing through the origin. The apparent
viscosity increases instantaneously with increasing shear rate. The yield
point, as determined by conventional calculations from the direct indi-
cating viscometer readings, is negative. See: Apparent Viscosity, Viscos-
ity, Bingham Model, Plastic Viscosity, Yield Point, Gel Strength.

Diluent Liquid added to dilute or thin a solution or suspension.