The initial proposal for abandoning a subsea field in the North Sea was to carry out the pre-abandonment work from the Light Well Intervention Vessel (LWIV) followed by the complete Plug and Abandon (P&A) operation conducted by a Mobile Offshore Drilling Unit (MODU). During the detailed design of the workscope, the four wells in the field were identified as through-tubing abandonment (TTA) candidates. To maximise the use of the LWIV and optimise the MODU sequence these TTA operations were planned to be executed from the LWIV. The TTA cement plug is installed by circulating cement down the production tubing and taking returns from the annulus to place the cement plug above the production packer and deep-set plug. An agitator tool is installed in the production tubing to improve the cement coverage in the annulus. As the LWIV does not have a permanently installed cementing system, a temporary system was fitted on the vessel which proved to be challenging given the deck limitations of the installation. Two of the four TTA candidate wells included a downhole gauge cable in the completion design across the zone that was required to be cemented. To ensure the long-term integrity of the TTA cement plug with the gauge cable, an expanding self-healing cement was utilised.

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