String Shot

This wireline-conveyed pipe recovery tool uses a precise quantity of explosive detonating cord to produce shock waves.
The string shot procedure involves applying left hand torque to the pipe string at the neutral pipe weight (in either tension or compression). The string shot is then positioned at the predetermined tool joint and detonated. The explosion produces much the same affect as an intense hammer blow and allows the joint to be unscrewed at the proper connection. The string shot method has been improved through years of research and experience to increase operating efficiency without damaging the pipe string.
In order to make up a proper string shot, certain factors must be determined.
  1. Pipe size, weight and condition
  2. Depth of back off
  3. Mud or fluid weight
  4. Well temperature

Factors 1,2 and 3 are needed to determine the size of the string shot and factors 3 and 4 are needed for the selection of the proper fuses and detonating cord. A string shot can be constructed that will readily run through an ID as small as 3/4 in. (19.1mm). It can also be run in the annulus to back off the pipe from the outside.

String Shot Applications

  • Back off pipe (inside and outside)
  • Release stuck packers or fishing tools, such as an overshot
  • Remove corrosion from pipe
  • Open perforations
  • Jump collars
  • Bump drill pipe loose in key seats (hard formations)
  • Remove jet nozzles in drill bits to increase rate of circulation

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