The Dialog backoff service applies left-hand torque in the pipe while the string shot is detonated. The torque is applied at the neutral weight.  The explosive percussion causes the joint to unscrew.  Using the collar locator, the backoff can be verified before coming out of the hole.

Criteria that affect the string shot construction are:

  • Pipe size and weight
  • Depth of stuck point and joint to be backed off
  • Fluid weight
  • Temperature
  • Ability to apply torque

The pipe size and weight, depth of stuck point and fluid weight are needed to determine the strength of the string shot and temperature is required to determine type of primacord and detonator.  A string shot can be run in the annulus and backoff pipe from the outside.

Other uses of the string shot include:

  • Releasing stuck packer
  • Overshot release
  • Removing corrosion or coatings from pipe
  • Opening blocked perforations
  • Jumping pipe collars
  • Removing jet nozzles in drilling bit