Page 332 - Shale Shakers Drilling Fluid Systems

314 SHALE SHAKERS AND DRILLING FLUID SYSTEMS

Oblong Mesh A screen cloth that has more openings per inch in one direction than in
the perpendicular direction. For example, a 70 x 30 mesh has 70 open-
ings per inch in one direction and 30 openings per inch in the perpendicu-
lar direction, creating a rectangular opening. The smaller opening dimen-
sion controls the sizing of spherical material. See.- Rectangular Screen.

Oblong Weave See.- Oblong Mesh.

OD Outside diameter of a pipe.

Ohm The measurement of resistance or electrical friction.

Oil-Based Drilling Fluid The term "oil-based mud" is applied to a special drilling fluid where
oil is the continuous phase and water is the dispersed phase. Oil-based
drilling fluid contains from l% to 5% water emulsified into the system
with lime and emulsifiers. Oil-based muds are differentiated from invert
emulsion muds (both water-in-oil emulsions) by the amounts of water
used, the method of controlling viscosity, the thixotropic properties, wall
building materials, and fluid loss. See.- Invert Oil Emulsion Drilling Fluid.

Oil Breakout Oil that has risen to the surface of a drilling fluid. This oil had been pre-
viously emulsified in the drilling fluid or may derive from oil-bearing
formations that have been penetrated.

Oil Content The oil content of any drilling fluid is the amount of oil in volume percent.

Oil Immersion An oil-filled construction where an electrical device has no electrical con-
nections, joints, terminals, or arcing parts at or above the normal oil level.

Oil Wet A surface on which oil easily spreads. If the contact angle of an oil droplet
on a surface is less than 90°, the surface is oil wet. See: Lipophilic, Wa-
ter Wet.

Oil-In-Water Emulsion Any conventional or special water-based drilling fluid to which oil has
Drilling Fluid been added. A drilling fluid in which the oil content is usually kept be-
tween 3% to 7% and seldom over 10% (it can be considerably higher).
Commonly called "emulsion mud." The oil becomes the dispersed phase
and may be emulsified into the mud either mechanically or chemically.
The oil is emulsified into fresh- or saltwater with a chemical emulsifier.

Overflow The discharge stream from a centrifugal separation that normally con-
tains a higher percentage of liquids than does the feed

Overflow Header A pipe into which two or more hydrocyclones discharge their overflow.

Overslung Field terminology denoting that the support ribs for the shaker screen are
located below the screen surface. See: Underslung.

Packer Fluid A fluid placed in the annulus between the tubing and casing above a
packer. The hydrostatic pressure of the packer fluid is used to reduce the
pressure differentials between the formation and the inside of the casing
and across the packer.

Panel Mounted Units Shale shaker screens mounted to a rigid frame.

Parallel Flow See: Laminar Flow.