1. n. [Drilling Fluids]
An item of solids-removal equipment that removes fine and ultrafine solids. It consists of a conical drum that rotates at 2,000 to 4,000 rpm. Drilling fluid is fed into one end and the separated solids are moved up the bowl by a rotating scroll to exit at the other end. Centrifuges generally have limited processing capacity (50 to 250 galUS/min) but are useful for processing weighted drilling fluids and can remove finer solids than can a hydrocyclone or shaker screens. They can also be used for water clarification or for processing oily cuttings.
See: closed mud system, dewatering
2. n. [Formation Evaluation]
A rapidly rotating flywheel on a vertical axle to whose rim is attached a series of tubes at one end, the other end being free to tilt upward and outward. At high speeds, the centrifugal force in the tubes is far greater than gravity. The centrifuge is used to expel fluids from core samples, either to clean them or to desaturate them for measurements of irreducible water saturation, resistivity index, or nuclear magnetic resonance properties. It can be used at multiple speeds to obtain a capillary pressure curve. Centrifuges are also used in studies of clay mineralogy, where micron-scale fractions are extracted from suspension and subjected to analysis by X-ray diffraction (XRD).