Mechanical blind back off is the procedure to intentionally break out stuck drill string by applying left hand torque and transmitting down hole. This is the last method to recover drill string because back-off position cannot exactly determine. One situation that I used to do the blind back of is when the perforating gun cannot be run into tubing string.
Procedure to Perform Blind Back Off Operation
1. Determine drilling parameters prior to get stuck if possible.
Pick up weight __ lb
Slack off weight __ lb
Rotating weight __ lb
2. Pick up drill string at 10% over the rotating weight. Apply 50% of make-up torque with left hand turn and lock TDS. Record how many turns. Slowly work string down for 5-10 minutes to transmit surface torque to the bottom. Weight while working should be between pick-up and slack off weight.
3. Repeat step#2 with 70%, 90%, 100%, 110% make up torque
4. The string should be back off while working down.
Note: The concept is to have overpull tension applied at each connection while left hand torque is transmitted into the drillstring. Once the drill string is worked, the torque will be transferred to the bottom connection of the well.