1. n. [Drilling Fluids]

The instrument used to measure viscosity and gel strength of drilling mud. The direct-indicating viscometer is a rotational cylinder and bob instrument, also known as a V-G meter. Two speeds of rotation, 300 and 600 rpm, are available in all instruments, but some are 6- or variable-speed. It is called "direct-indicating" because at a given speed, the dial reading is a true centipoise viscosity. For example, at 300 rpm, the dial reading (511 sec^-1) is a true viscosity. Bingham plastic rheological parameters are easily calculated from direct-indicating viscometer readings: PV (in units of cP) = 600 dial - 300 dial and YP (in units of lbm/100 ft²) = 300 dial - PV. Gel strength is also directly read as dial readings in oilfield units of lbm/100 ft².

Synonyms: Fann viscometer

See: Bingham plastic model,  deflocculant,  gel strength,  Herschel–Bulkley fluid,  Newtonian fluid,  non-Newtonian fluid,  plastic viscosity,  power-law fluid,  rheological property,  yield point