Using chemical solutions to recover loose material in subsea tie-back pipeline

By Erika Johana Tovar, Halliburton

This article contains highlights of paper SPE-222871, “Recovering Loose Material During Decommissioning of Subsea Tie-Back Pipeline Using Chemical Solutions in the Norwegian Sea: A Case Study”, by J. Skorpen, Equinor; E.J. Tovar, E. Byremo, O. Aamodt, A. Groven, R. Eliassen, Halliburton, prepared for the ADIPEC conference and exhibition held in Abu Dhabi, UAE, Nov 4-7, 2024. For more details, find paper in OnePetro.org

Engineered and customized chemical solutions have demonstrated to be effective with debris and solid material transportation, even in pipelines. This case study shows the successful implementation during decommissioning operations in the Norwegian Sea of a superior gel system designed and adapted for low temperatures to recover several cap-screws lost in subsea flowlines after pigging operations were performed, avoiding any potential consequences of the loose material to the assets.

Challenge

During the pigging operations, it was discovered that rear module had disconnected from the joint assembly of four dual module pigs and in one more, the front module had disconnected as well from the joint assembly. In total, 28 cap-screws were missing, left in the subsea flowlines.

Disconnected cap screws with wear damage on the threads

Dual Module pigs with disconnected articulated joint assembly

Customized Solution

The main concern was to ensure that no damage would be caused in the future by the loose material in the flowlines, generating additional operational costs and affecting the integrity of the full system. Recovering loose material with magnets was considered and a trial was done to determine whether magnets would pick up any loose material. However, the magnetic attraction was very low and would not allow safe pick-up of the cap screws.

Inspection with camera and ultrasonic tool were performed and confirmed that no immediate damage was caused by the cap-screws, but there would be potential risk if they were left permanently in the system. Removal was necessary.

Therefore, a MegaGel fluid system was used as a viscous medium to suspend the cap-screws and recover them to surface. The fluid system features high static gel strength, high debris suspension capacity and it was designed to work in the low temperatures of the Norwegian Sea, reducing the risk of hydrates formation in the subsea flowlines.

As a result, 19 cap-screws were recovered successfully. Only 9 cap-screws remain unaccounted for, which could have been ejected to the open-sea pig cage, recovered to surface but not noticed, discharged to closed drain and/or remain in the flowline system without serious impact.

The collaboration and engineered solutions enabled the safe execution of contingency actions within the time frame available, using custom pipeline chemical solutions to enhance the decommissioning operations success.