DECOMMISSIONING
Comparative Assessment of Decommisioning Options
Assessing the decommissioning options
most appropriate and a derogation case was submitted to, and subsequently approved by OSPAR. Te jacket footings will remain in place although the jacket will be removed to a height of approximately 44m above the sea bed and brought onshore for reuse, recycling or disposal purposes. Te drill cutting piles will be left in their original location at the jacket footings, to decay naturally over a period of time. Te transparency and robustness of the
process made it clear to the regulator how the decision to apply for derogation had been reached and what the implications were for health & safety, shipping & navigation and fisheries in both the short- and the long-term.
COMPARATIVE ASSESSMENT FOR INFIELD PIPELINES Another example of the use of comparative assessment involves 16 infield pipelines located within a designated conservation area and included in a proposed decommissioning programme in the southern North Sea. Te operator, Conoco Phillips, had agreed to remove all the topsides, jackets and associated subsea infrastructure, but was examining whether or not it could leave the pipelines and mattresses in-situ. Conoco
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Phillips engaged BMT Cordah to carry out a comparative assessment for decommissioning the pipelines in situ to help determine the preferred option for this and future decommissioning programmes. Te comparative assessment concluded that decommissioning with minimum intervention was most appropriate. Mattresses would remain in situ, cut pipeline ends to have rock- placement, with no additional rock- placement along the pipeline length. In this situation, full removal was deemed least appropriate.
Although comparative assessment is not fool-proof, it will provide robust outcomes if appropriate scoring and ranking systems are employed and the process is facilitated correctly. Problems occur because either:
l Evaluation criteria or options are ‘soft’ and require judgement calls typically where data is not available.
l Criteria are described inadequately, leading to inconsistent use and interpretation.
l Criteria are used that do not differentiate the options and are irrelevant to the decision being made.
l Te focus is erroneously placed on the
method rather than the outcomes and consequences of the different options.
l Te assessment is overcomplicated, including too many or irrelevant options.
l Tere is inadequate technical knowledge of the options and their differentiators.
Te use of comparative assessment in decommissioning programmes can deliver easily accessible, robust findings to comply with the regulatory framework or to help deliver best practice. Its scalable nature means that operators can take an incremental approach to comparative assessment and start with the most simple and qualitative approach, moving only to the more complex and quantitative methods if it is deemed necessary. With expenditure on decommissioning in the North Sea alone expected to exceed £35 billion over the next 25 years, the delivery of comparative assessment will be a key part of the mix. l
Dr Joe Ferris is Associate Director, BMT Cordah (Scotland) and Johnny Tjea is president director, BMT Asia Pacific (Indonesia).
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