1. n. [Drilling Fluids]

A property of fluids and slurries that indicates their resistance to flow, defined as the ratio of shear stress to shear rate. Viscosity can be expressed mathematically as follows: Poise is the unit for viscosity, equivalent to dyne-sec/cm². Because one poise represents a high viscosity, 1/100 poise, or one centipoise (cp), is used for mud measurements. One centipoise equals one millipascal-second. Viscosity must have a stated or an understood shear rate in order to be meaningful. Measurement temperature also must be stated or understood.

See: bentonite,  Bingham plastic model,  breaker,  Brookfield viscometer,  capillary tube viscometer,  carboxymethylcellulose,  centipoise,  derrickman,  direct-indicating viscometer,  funnel viscosity,  gel strength,  gyp mud,  Herschel–Bulkley fluid,  high-pressure, high-temperature viscometer,  Marsh funnel,  mud additive,  Newtonian fluid,  non-Newtonian fluid,  pill,  plastic fluid,  power-law fluid,  pseudoplastic,  PVT,  rheological property,  rheology,  shear rate,  shear stress,  VG meter,  yield