Conditions for a successful back-off:
a) The string shot strength should be sufficient to back-off the pipe without causing damage to the pipe or the connection. The size of the shot should be advised by the Logging Contractor, and depends upon the depth of the back-off attempt, and whether the back-off is in the drill pipe or drill collars.
Successful back-off between drill collars is statistically low. The best string joints for back-off therefore is at the X-over from drill collars to HWDP (if unstuck . . .