Plastic Viscosity (PV)
Definition - What does Plastic Viscosity (PV) mean?
Plastic viscosity is the resistance to the flow of a fluid. It is caused by the mechanical friction within the drilling mud due to interaction between solids, the liquids and the deformation of liquid that is under shear stress. It is an important property of drilling mud that must be kept within the designed limits for efficient drilling.
Petropedia explains Plastic Viscosity (PV)
Plastic viscosity is expressed in centipoise (cP).
It is easy to measure plastic viscosity with the help of a viscometer, which helps to estimate the shear rate at 600, 300, 200, 100, 6 and 3 rpm (rotations per minute). The plastic viscosity of a fluid is calculated by subtracting the reading at 600 rpm from the reading at 300 rpm. For example, if the reading in the viscometer at 600 rpm is 56 and the reading in the viscometer at 300 rpm is 35, then the plastic viscosity of the fluid is:
Plastic Viscosity = 56 – 35 = 21 cP
In normal drilling conditions, the mud weight is directly proportional to the plastic viscosity, which means that if the weight of the mud is higher, then the fluid would be viscous, i.e., its plastic viscosity will be high.
A check needs to be performed on the increase in the trend graph of plastic viscosity without the change in the mud weight, which means that ultra-fine drill solid content has increased in the mud system. Moreover, if an oil base mud is used, then the emulsified water in the oil base drilling fluid acts similar to ultra-fine drill solid content and therefore dramatically increases the plastic viscosity of fluid flow.