Bentonite Rheology: R600, R300, PV and YP

R600 and R300 are the starting measurements

R600 and R300 are direct viscometer readings at 600 and 300 r/min. Together they allow calculation of plastic viscosity, yield point, YP/PV and apparent viscosity.

Plastic viscosity — PV

PV = R600 − R300

PV is conventionally reported in cP and represents the viscous contribution of the suspension under the test condition.

Yield point — YP

YP = R300 − PV

YP is conventionally reported in lb/100 ft² and is useful for describing the structure developed by the suspension. A high YP is not automatically beneficial; its relationship to PV must also be considered.

YP/PV ratio

YP/PV = YP ÷ PV

The API-oriented maximum is 3 and the OCMA-oriented maximum is 6.

Apparent viscosity — AV

AV = R600 ÷ 2

AV is useful for general fluid interpretation but is not one of the principal Clause 9 bentonite acceptance limits.

Worked example

For R600 = 38 and R300 = 25: PV = 13 cP, YP = 12 lb/100 ft², YP/PV = 0.92 and AV = 19 cP.

Invalid data checks

If R300 is greater than R600, verify the readings and instrument conditions. If R600 equals R300, PV is zero and YP/PV is undefined.