Differential pressure is the key to drilling with a mud motor. Knowing your off-bottom pressure, on-bottom pressure and stall point will increase your rates of penetration and ensure maximum drilling hours with the motor.
All mud motors have a flow range based on the power section. The motor will run most effectively on the upper end (70% to 85% of maximum flow capacity) of the power section. The motor specification sheet will provide the bit speed, rotary torque and differential pressure based on the flow rates of the power section:
The motor produces higher bit speeds, higher rotary torque and allows for higher differential pressures on the upper end of the power section. The higher rotary torque and higher bit speeds will help maximize rates of penetration and keep the motor from stalling out. If flow rates are too low, the motor produces lower bit speeds, less rotary torque and less differential pressure allowing the motor to stall out easily.
Mud pressures should be monitored on the rig’s mud pressure gauge:
Stall Point Pressure
which causes the drill bit and internal movement of the power section to stop working.
Stalled Out Pressure
Optimum Drilling Pressure
The mud motor runs most effectively and maximizes rates of penetration just below the stall point.