Coiled-Tubing Fishing Operations

Various factors can cause a string of coiled tubing (CT) to become lost in the hole. Most partings, however, are the result of a straight tension pull that exceeds the tensile strength of the tubing or by a bending break caused by compression of the CT inside the tubing or casing.

Parting caused by a straight overpull of the coil exhibits a neck-down, or tapering, of the coil from the nominal OD to a smaller OD at the break point.

A bending break can occur either as the coil bends (or runs past and folds back onto itself) in the tubing or casing or as pickup is applied. Commonly referred to as a shepherd’s hook, this bent-over or collapsed condition prohibits the use of an overshot (OS) because the lack of a clean profile prevents proper engagement of the OS with the top of the CT fish.

To engage the coil, the OS is set up to pass over the tapered length to an area with a full OD. This positioning enables the grapples to bite onto the tubing effectively. Preparatory runs with a washover/milling assembly may be necessary to dress off the damaged area and return it to a nominal OD for correct engagement.

The cutter or snipper overshot (SOS) can be used in a variety of circumstances. When running on CT, this catch- and-cutting mechanism enables washing over the top of the fish, usually 10 ft (3 m) at most. This process allows optimal OD engagement of the grapples below a damaged area. Overpull is applied to engage the catch grapple on the CT. If the CT frees up, it can be retrieved from the hole. If continued pull is exerted beyond a preset shear load, the lower cutting grapple is activated, and the cut is achieved at a measured overpull that does not exceed the tensile limitation of the work string. The damaged top section of parted CT is removed, leaving around fish neck ID for subsequent fishing or cutting runs. The SOS has also been used with jointed tubing as a cutting and retrieval tool to recover several thousand feet of CT in a single trip.

The continuous overshot (COS) is used to retrieve CT that has parted in the hole. When fishing CT, the COS can be run with either threaded tubing or CT work strings. As a second run to the SOS the COS can be run in conjunction with a high-pressure packoff assembly. This configuration maintains circulation integrity for cutting the tubing with the radial cutting torch (RCT) tool or for releasing the bottomhole assembly if ball-activated tools are in place below the cut point. The COS uses a catch grapple that is similar to that of the SOS. Once contact is made with the top of the fish, the OS moves freely downward over the CT. When the desired length has been swallowed, upward movement engages the grapples, and pull force is exerted. If this force cannot move the fish, a pull force strong enough to exceed the tensile of the CT is required to pull it apart at the grapple bite area.