Functions of Drilling Fluids
Results of extensive research and in the field show that penetration rate and its response to weight on bit and rotary speed is highly dependent on the hydraulic horsepower reaching the formation at the bit. Since the drilling fluid flow rate sets the system pressure losses, and these pressure losses set the hydraulic horsepower across the bit, it can be concluded that the drilling fluid is as important in determining drilling costs as all other “man-controllable” variables combined. Considering these factors, “an optimum drilling fluid is a fluid properly formulated so that the flow rate necessary to clean the hole results in the proper hydraulic horsepower to clean the bit for the weight and rotary speed imposed to give the lowest cost, provided that this combination of variables results in a stable borehole which penetrates the desired target.”
A properly designed drilling fluid will enable an operator to reach the desired geologic objective at the lowest overall cost. A fluid should enhance penetration rates, reduce hole problems and minimize formation damage.
