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Fishing with Overshots

The following guidelines should be considered when fishing with overshots:

  • A pack-off should be installed if circulation through the fish is required before POOH.
  • If the hole size is larger than the overshot OD, an oversized guide should be considered.
  • If the pipe is lying in a recess or against the side of the hole, consider a hook wall guide or bent joint.
  • If the fish cannot be engaged, consider an extension sub and a milling guide. A milling guide shall always be run with a basket grapple.
  • To catch an upset or box section of a tool joint, a basket grapple with long catch stop shall be considered to be able to disengage the fish for unexpected reasons.
  • To catch a coupling with a ruptured piece of pipe engaged in its upper end, a basket grapple with short catch stop, which has a double set of wicker of two different IDs shall be considered.
  • The penetration of the fish into the overshot shall be limited in order to facilitate releasing it from the fish.
  • An overshot can be used to back off as left hand torque tightens the grapple bite on the fish so right hand rotation can release the grapple.
  • Unless an upward strain is maintained, the fishing string shall never be rotated to the right while an overshot is engaged on the fish, other than when attempting to come off the fish.
  • Before the start of releasing operations slack off until slight compression at overshot. Release with right hand torque.
  • When lowering the overshot over the fish, once a pressure increase is noted, circulation shall be stopped in order to prevent damaging the seal/packer. Bleed off any pressure trapped prior to engaging the fish.
  • When the fish has been freed, the well shall be flow checked and circulated bottoms up as required, if circulation is possible through the fish.
  • Make up circulating sub on fishing assembly.
  • Start to rotate using chain tongs for rotating slowly.
  • After fish is engaged, do not turn to the right as this will generally release overshot.
  • Top of fish usually needs washing - but beware of washing away pack-off.

Generic Procedure

1. Before engaging the fish, establish up/down and rotating weight.

2. With the overshot directly above the fish, a combination of rotating and lowering shall result in the following:

The guide directs the fish into the overshot.

The fish can easily pass through the grapple because of its helical shape and mode of rotation.

Too much rotation can damage/wear the grapple.

3. If the basket grapple used is not a long catch stop type, USE a stop to stop the grapple going completely over the upset of the fish. If the grapple goes over the upset of the fish, it would be almost impossible to release the overshot from the fish.

4. When the fish is properly located in the overshot, EXERT an upward pull. ALLOW pull to ‘soak’ to allow setting of the grapple and penetration into fish. From this point onwards, MAINTAIN positive overpull on fish at all times. The grapple will be contacted by the upward taper in the bowl and the fish held securely. The pack-off rubber seals around the fish enabling fluid to be forced down through the fish.

5. By lowering the string weight or bumping down against the fish, the grapple can be freed from the bowl. By slowly rotating to the right and slowly raising the string, the spiral grapple unwinds or the basket grapple expands disengaging the string from the fish.

Overshot with Spiral Grapple

Spiral grapples shall be used when the diameter of the fish is near to the maximum OD of the overshot.

Overshot with Basket Grapple and Grapple Control Packer

Basket grapples shall be used when the fish diameter is below the maximum catch size of the overshot.

Fishing Procedure with Overshot

1. RUN fishing assembly to top of fish (TOF).

2. CIRCULATE to clean off TOF (beware of washing away pack-off)

3. TAKE up/down and rotating weights. MARK point of start moving up, start moving down and ESTABLISH neutral point

MEASURE stretch and compression.

4. LOWER overshot slowly to touch TOF.

5. CHECK depth against points established in Step 3.

6. START rotation to right and STOP circulation.

7. RUN fishing assembly over fish until ‘swallow’ is full engaged.

8. STOP and OBSERVE weight indicator for weight decrease.

9 STOP rotation and RELIEVE torque in string.

10. PULL UP slowly and OBSERVE weight indicator for weight increase (to confirm engaged fish).

11. CIRCULATE bottoms up without rotation to clean hole prior to POOH with fish.

12. POOH with fish (do not rotate string, no jerking).

Procedure for Fish Release

1. ATTEMPT with light compression only (2 000 - 5 000 lbs).

2. BUMP down against overshot to release grapple.

3. ROTATE fishing assembly to right.

4. RAISE assembly gradually until top of overshot is clear of fish.