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 and solids, the liquids and the deformation of liquid which 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)
It is easy to find out Plastic Viscosity with the help of a viscometer. Viscometer helps in estimating the shear rate @ 600, 300, 200, 100, 6 and 3 rpm (rotations per minute). Plastic viscosity of a fluid is calculated by subtracting reading at 600 rpm from the reading at 300 rpm. For example, if the reading in the viscometer @ 600 rpm is 56 and the reading in the viscometer @ 300 rpm is 35, therefore, plastic viscosity of the fluid is:
Plastic viscosity = 56 – 35 = 21 Centi Poise
Plastic viscosity is expressed in Centi Poise (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 thereby dramatically increases the plastic viscosity of fluid flow.