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Oilfield Glossary
Oilfield Glossary
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Fann viscometer

Illustration of a direct-indicating viscometer
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1. n. [Drilling Fluids]
Also known as direct-indicating viscometer or V-G meter, an instrument used to measure viscosity and gel strength of drilling mud. The direct-indicating viscometer is a rotational cylinder and bob instrument. 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 lb/100 ft2) = 300 dial - PV. Gel strength is also directly read as dial readings in oilfield units of lb/100 ft2.