Question

What is the difference between the Plastic Viscosity and Apparent Viscosity of a drilling fluid?

Answer 1

PLASTIC VISCOSITY :

A parameter of the Bingham plastic model. PV is the slope of the shear stress vs shear rate line above yield point. PV represents the viscosity of drilled fluid when extrapolated to infinite shear rate on the basis of the mathematics of the Bingham model.( Yield point , YP is the other parameter of the model ) . A low PV indicates that the fluid is capable of drilling rapidly because of the low viscosity of fluid exiting at the bit.

High PV is caused by a viscous base fluid and by excess colloidal solids. To lower PV , a reduction in solids content can be achieved by dilution of drilling fluid.

APPARENT VISCOSITY :

The viscosity of a fluid measured at a given shear rate at a fixed temperature. In order for a viscosity measurement to be meaningful , the shear rate must be stated or defined.