WOB / RPM
PDC bits tend to drilling with low WOB and high RPM.
They are also found to require higher torque than roller cone bits.
The general recommendation is that the highest RPM that can be achieved should be used.
Although the torque is fairly constant in shale sections the bit will tend to dig in and torque up in sandy sections. When drilling in these sandy sections, or when the bit drills into hard sections and penetration rate drop, the WOB should be reduced but should be maintained to produce a rotary torque at least equal to that of a roller cone bit.
Too low a WOB will cause premature cutter wear, possible diamond chipping, and a slow rate of penetration.
Mud Properties
The best ROP results have been achieved with oil-based muds but a good deal of success has been achieved with Water Based Mud.
Reasons for the improved performance in oil based mud have been attributed to increased lubricity, decreased cutter wear temperature, and preferential oil wetting of the bit body. The performance of PDC bits in respect to other mud properties is consistent with that found with Roller Cone Bits i.e. increase in mud solids content or mud weight decreases ROP.
Hydraulic Efficiency
The effects of increased hydraulic horsepower at the bit are similar to their effect on Roller Cone Bits. However, manufacturers will often recommend a minimum flow rate in an attempt to ensure that the bit face is kept clean and the cutter temperature is kept to a minimum. This requirement for flowrate may adversely affect the optimization of HHP.
