Why motors backoff (when stalled) and how to prevent it:
A mud motor backoff between the bent sub and the stator is caused simply by Newton's third law of Physical Science. For every action there is an equal and opposite reaction. Following is an explanation of what happens and how to prevent it. The mud motor is stalled, the reaction is physical force (stall torque as seen on the spec sheet) which is now trapped between the bent sub connection and the stator connection (due to the hydraulic/mechanical force of the rotor on the stator rubber). This force is to the left (counter clock wise) which you will also notice when sliding that your toolface moves left as you increase differential pressure. Same thing but now it is at full force (stall torque) and trapped (nothing is moving counter or clockwise). How to never break this connection and backoff the connection due to stall:
- Do not panic, be mindful, this is a solvable problem. Do not pull the motor off bottom!
- Turn off the pump. Do not idle down, turn it off.
- Bleed off pressure (slowly opening the fillup line works great)
- Turn top drive slowly to the left releasing any torque in the string
- Ease off bottom
Squat/Axial Test Procedures:
- To begin test, the mud motor needs to be drained.
- The BHA remains in the table for the first measurement.
- With the bit breaker and BHA securely in the rotary table, slack off on the BHA until the motor body above the bit box ceases to move down
- Take your first (Squatted) measurement with the small jaws on the caliper, which are called the internal jaws. Place one jaw on the inside of the end nut (B) and one jaw on the wrench slot shoulder of the radial stop (D).
- Record your squatted reading (distance C). Use only 3 decimal places, the correct measurement would be 2.873".
- Leaving the caliper in the 2.873" measurement distance. Re-zero the caliper by pushing the zero button.
- Lift the BHA out of the rotary table. Have the rig personnel press down on each side of the bit breaker until internal driveshaft is fully extended.
- Dial calipers are at zero re-measure the exact same spot this is your squat or axial measurement.