Robust and Efficient MAH & SECE Management in Decommissioning; Enabling a Fit-For-Purpose Transition to Post-Cessation of Production (CoP) Operations

Abstract OEUK's decommissioning insight report published in 2023 (ref.1) identifies a reduction in producing assets from 283 in 2023 to just 103 in 2030. This represents an unprecedented volume of decommissioning activities. Every installation has safety and environmental critical elements (SECE), which prevent or mitigate the consequences of an MAH event. However, as CoP is reached and subsequent decommissioning scopes carried out, risks are reduced, and some MAH scenarios eliminated, or materially reduced in magnitude. Commensurate with this, some SECEs become redundant, or only require reduced functionality. It is DNV's experience that many SECEs remain classified as safety critical throughout decommissioning, with the majority of SECEs removed/de-classified once the installation has been made hydrocarbon free (including wells and pipelines). This results in an unnecessary maintenance burden on SECEs throughout this period. Instead of this, classification of SECEs can be linked to key decommissioning milestones i.e. once associated MAHs risks are eliminated. In doing so, a large maintenance burden is removed and subsequent efficiency savings made on the wider decommissioning programme. To be successful, planning work must be completed in advance of CoP. This should start with defining the key decommissioning milestones and then mapping the SECEs to these – noting that some SECEs will need to remain through to dismantlement and beyond e.g. NAVAIDs, and some may only be partially removed, remaining as safety critical but with reduced functionality. A checklist should be produced for each SECE, defining the requirements that must be completed prior to removing the safety critical status of that equipment. Thought must also be given to the safety case; specifically the required number and timings of revisions. Limiting the number of revisions is key to an efficient process, and so a decommissioning safety case should be drafted in advance, detailing the milestone process described above and outlining the milestone each SECE change is linked to. This way one revision of a decommissioning safety case can cover CoP, DFPV (or equivalent), and P&A, up to and including process hydrocarbon free and minimum manning. Dismantlement will likely require a new revision of a safety case. The trigger for revising the safety case must be identified. However, the first steps of decommissioning post CoP are all reversible (not different to e.g. summer turn arounds) and therefore are covered by the operational safety case. It is possible that neither CoP nor DFPV will require a new revision of a safety case. Perhaps, therefore removal of the first SECE during decommissioning activities may be the trigger for a material change. The approach described above can bring about large efficiency savings in both regulatory compliance and offshore workload, throughout the duration of the decommissioning programme.