Claxton Engineering Services Ltd, an Acteon company, has completed the first rigless removal of a stuck bottom hole assembly (BHA). The work was completed during a slot recovery operation using an innovative approach at Maersk’s Tyra East field in the Danish sector of the North Sea.
The well was drilled in the 1980s and, during construction, the BHA had become stuck in the conductor pipe and prevented well completion. Claxton used its slot recovery methodology and tooling, specialist cutting equipment and a dive support vessel to solve the issue.
The programme began with the deployment of a specialist casing cutting system to remove a section of the conductor, which left the stuck BHA intact but exposed. This called for modification of the cutting equipment and the subsea application of a system that is normally used on the surface.
Once the conductor had been cut and removed, Claxton engineers prepared a specialised lifting device using an air hoist on deck deployed through an A-frame, while divers clamped the lifting gear to the BHA. The BHA was too heavy to recover in one piece and had to be cut subsea. This involved using two sizes of diamond wire-cutting machine: the smaller to sever only the exposed BHA, and the larger to cut simultaneously through the remaining conductor stump and the BHA. The cut needed to give a smooth and flush surface on the end of the conductor. Once the cutting machine had sliced through the conductor and the BHA, the top section was recovered.
During planning, the orientation of the remaining BHA relative to the conductor stump was uncertain. Claxton created a unique whipstock with a slot beneath the landing plate that would enable it to capture the exposed part of the BHA securely in any orientation. The top half of the whipstock would rotate on this base and enable the new well to be kicked off in any direction. Claxton’s experience in whipstock design ensured an effective design for the project.