Page 306 - Shale Shakers Drilling Fluid Systems

288 SHALE SHAKERS AND DRILLING FLUID SYSTEMS

Chemicals In drilling fluid terminology, a chemical is any material that produces
changes in the low-shear-rate viscosity, yield point, gel strength, fluid loss,
pH, or surface tension.

Choke An opening, aperture, or orifice used to restrict a rate of flow or discharge.

Chromate A compound in which chromium has a valence of 6 (e.g., sodium dichro-
mate). Chromate may be added to drilling fluids either directly or as a
constituent of chrome lignites or chrome lignosulfonates to assist with
rheology stabilization. In certain areas, chromate is widely used as an
anodic corrosion inhibitor, often in conjunction with lime.

Chrome Lignite Mined lignite, usually leonardite, to which chromate has been added and/
or reacted. The lignite can also be causticized with either sodium or
potassium hydroxide. The chrome lignite is used for rheology stabiliza-
tion and filtration control of the drilling fluid.

Circular Motion A shale shaker screen moves in a uniform circular motion when the vi-
brator is located at the center of gravity of the vibrating basket.

Circulation The movement of drilling fluid through the flow system on a drilling or
work-over rig. This circulation starts at the suction pit and travels through
the mud pump, drill pipe, bit, annular space in the hole, flow line, fluid
pits, and back again to the suction pit. The time involved is usually re-
ferred to as circulation time. See: Reverse Circulation.

Circulating Sytem All of the drilling fluid moving through the surface system and downhole.

Circulation Rate The volume flow rate of the circulating drilling fluid, usually expressed
in gallons per minute or barrels per minute. See: Flow Rate.
Clabbered A slang term commonly used to describe moderate to severe floccula-
tion of drilling fluid due to various contaminants. See: Gelled Up.

Clarification Any process or combination of processes, the primary purpose of which
is to reduce the concentration of suspended matter in liquid.

Clay (1) A soft, variously colored earth, commonly hydrous silicates of alumina,
formed by the decomposition of feldspar and other aluminum silicates.
Clay minerals are essentially insoluble in water but disperse under
hydration, grinding, or velocity effects. Shearing forces break down the
clay particles to sizes varying from sub-micron to 100 microns or larger.
(2) Physical Description: Solid particles of less than two micrometer
equivalent spherical diameter. See.- Attapulgite Clay, Bentonite, High-Yield
Clay, Low-Yield Clay and Natural Clays.

Clay Extender Substances, usually high molecular weight organic compounds, which
when added in low concentrations to bentonite or other specific clay slur-
ries, will increase the low-shear-rate viscosity of the system. An example
would be polyvinyl acetate-maleic anhydride copolymer. See.- Low Solids
Drilling Fluids.

Clay-Size Particles See.- Clay.

Close Loop Mud Systems A drilling fluid processing system that minimizes the liquid discard. Usu-
ally as much as possible of the liquid phase normally separated with
drilled solids is returned to the active system.