Page 323 - Shale Shakers Drilling Fluid Systems

GLOSSARY 305

Hydrostatic Pressure Head The pressure exerted by a column of fluid, usually expressed in pounds
per square inch. To determine the hydrostatic head in psi at a given depth,
multiply the depth in feet by the density in pounds per gallon by the
conversion factor, 0.052.

Hydroxide A designation that is given for basic compounds containing the OH- radi-
cal. When these substances are dissolved in water, the pH of the solu-
tion is increased. See.- Base, pH.

Hygroscopic The property of a substance enabling it to absorb water from the air.

ID Inside diameter of a pipe.

Impeller A spinning disc in a centrifugal pump with protruding vanes used to
accelerate the fluid in the pump casing.

Indicator Substances in acid-base titrations that, in solution, change color or be-
come colorless as the hydrogen ion concentration reaches a definite
value. These values vary with the indicator. In other titrations, such as
chloride, hardness, and other determinations, these substances change
color at the end of the reaction. Common indicators are phenolphthalein,
methyl orange, potassium chromate, and so forth.
Inertia The force that makes a moving particle tend to maintain its same direc-
tion, or a particle at rest to remain at rest.

Inhibited Drilling Fluid A drilling fluid, having an aqueous phase with a chemical composition,
which tends to retard and even prevent (inhibit) appreciable hydration
(swelling) or dispersion of formation clays and shales through chemical
and/or physical reactions. See: Calcium Treated Drilling Fluids, Salt-
water Drilling Fluid.

Inhibited Mud See: Inhibited Drilling Fluid.

Initial Gel See: Gel Strength.

Inlet The opening through which the feed mud enters a solids control device.
See: Feed Inlet, Feed Opening.

Interfacial Tension The force required to break the surface definition between two immis-
cible liquids. The lower the interfacial tension between the two phases
of an emulsion, the greater the ease of emulsification. When the values
approach zero, emulsion formation is spontaneous. See: Emulsion, Sur-
face Tension.

Intermediate (Solids) Particles whose diameter is between 250-2000 microns.

Interstitial Water Water contained in the interstices or voids of formations.

Intrinsic Safety A feature of an electrical device or circuit in which any spark or thermal
effect from the electrical device or circuit is incapable of causing igni-
tion of a mixture of flammable or combustible material in air.

Invert Drilling Fluid See: Invert Oil Emulsion Drilling Fluid.

Invert Oil Emulsion Drilling A water-in-oil emulsion where water (sometimes containing sodium or
calcium chloride) is the dispersed phase, and diesel oil, crude oil, or some