Backing off Procedures
The string shot size shall be determined by the Logging Engineer so that it will be large enough to back-off the joint to be released without splitting the pipe. If the pipe does not back-off after the first shot, the charge can be increased on subsequent runs.
The physical size of the primer cord bundle shall be confirmed small enough to pass through the minimum pipe ID.
Weight, Torque and Turns on the String
Ideally the neutral point of the string weight distribution should be at the back-off point . . .