Last month, we started a discussion on drilling fluids viscosity with a look at some terms drillers should know and the basics of viscosity testing. This month, we get into detail to help drillers understand how viscosity affects mud pump performance.
First off, know that all mud pumps are calibrated with water at sea level which, to remind readers, has a 26s viscosity. That means that, at 40s viscosity, you lose 10-15% capacity; at 60s viscosity, up to 30%; and at 80s viscosity, up to 50%. Operators need to take this into account when calculating flow requirements. The gauge on the control panel of the drill does not automatically calculate viscosity, nor is there a magic dial on the pump to take viscosity into account. It is up to us to account for this and apply it correctly.