Plastic Viscosity (PV) is the fluid’s resistance to flow. According to the Bingham plastic model, the PV is the slope of the shear stress and the shear rate. In the field, we can obtain the PV from a viscometer. Typically, the viscometer is used to measure shear speeds at 600, 300, 200, 100, 6, and 3 revolutions per minute (rpm).

We can calculate the PV from the difference between the 600 and 300 rpm reading.

The formula looks like this: Plastic Viscosity (PV) = Reading at 600 rpm – Reading at 300 rpm

The unit of PV is Centi Poise (CP)

For example, you have these values ​​from a viscometer.

Reading at 600 rpm = 56

Reading at 300 rpm = 35

Plastic viscosity (PV) = 56 – 35 = 21 CP

Any increase in solids content in the drilling mud such as barite, drill solids, lost circulation material, etc. will result in higher plastic viscosity. To reduce the PV, you must reduce the solids content which can be achieved through the use of solids control equipment and/or dilution of drilling mud with base fluid. With increasing temperature while drilling deeper, the plastic viscosity of the drilling mud will decrease because the viscosity of the base fluid decreases.

Typically, the higher the mud weight, the higher the PV. However, if you have an increasing PV trend with constant mud weight, it means that there is an increase in the ultrafine drill solids content in the mud system. Also, if you are using oil-base mud, be aware that the emulsified water in the oil-base drilling fluid will act like a solid and dramatically increase the viscosity.

Various impacts of photovoltaics on the drilling operation are as follows:

Equivalent Circulating Density (ECD) – The more HP you have, the higher the ECD.

Surge and Sweep Pressure – The PV has the same effect as the ECD. If you increase the HP, it will increase the boost and swab pressure.

differential sticker – The probability of differential sticking will increase, especially in water-based muds, when the plastic viscosity increases due to increases in solids content.

Rate of Penetration (ROP) – The ROP will be directly affected by the plastic viscosity. If you drill a well with high PV drilling mud, you will be drilling with a slower ROP than with low PV mud.