Friday, October 9, 2015

Drilling fluid process glossary O

Oblong mesh. A screen cloth that has more openings per inch in one direction than in the perpendicular direction. For example, a 70×30 mesh has 70 openings per inch in

one direction and 30 openings per inch in the perpendicular direction, creating a rectangular opening. The smaller opening dimension 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 type of drilling fluid in which oil is the continuous phase and water the dispersed phase.

Oil-based drilling fluid contains from 1 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 previously 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 percentage.
Oil immersion. An oil-filled construction in which an electrical device has no electrical connections, 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, water wet.
Oil-in-water emulsion drilling fluid. Any conventional or special waterbase drilling fluid to which oil has been added. A drilling fluid in which the oil content is usually

kept between 3 and 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 freshor saltwater with a chemical emulsifier
Overflow. The discharge stream from a centrifugal separation that normally contains 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.