Operators around the world are reviewing their aging assets, and are coming to clench with the reality that some offshore fields are no longer economically viable. The North Sea and the Gulf of Mexico have seen numbers of decommissioning activities. In other regions, decommissioning activities had started to emerge, now and in the coming years. Decommissioning, an easy-look-but-massive-task come with unique challenges and cost ranging in the billions. Delivering an effective decommissioning especially when dealing with deep-water operations are paramount as to secure the economic value from the assets. Health, Safety and Environmental (HSE) concerns are always vital in any decommissioning process. The target is to effectively reduce the long term risks to other benefactors of the sea while the associated short term risks to those responsible for decommissioning operations are minimized. A major part of any decommissioning project is the decommissioning of subsea pipelines including the flowlines and risers.
Referring to a field case example from one of PETRONAS's deepwater field decommissioning project in Atlantic Ocean, a numbers of techniques had been considered for decommissioning of subsea pipeline system which sited in 700m to 960m water depth, ranging from preservation for potential future use, leaving in-situ or full recovery. Noted that each subsea pipeline decommissioning technique should be considered on its own merit, thus the assessment of each decommissioning technique had been based on many parameters, amongst others, size of pipeline, type of pipeline (e.g. single pipe, pipe-in-pipe, flexible), type of fluid in the pipeline, operational environment (location), production history, Inspection, Repair and Maintenance (IRM) records, HSE considerations, connection to other facilities, technical feasibility (including potential use of advanced technologies), regulatory authorities requirements and socio-economic considerations.
This paper covers only at specific of PETRONAS deepwater subsea flowlines and risers decommissioning experiences. It outlines the activities done starting from desk top activities (e.g. planning and concept) up to operational activities (e.g. pigging, flushing, cleaning, disconnection, retrieval or leaving in-situ). Different considered scenarios are discussed and potential advantages and disadvantages of each scenario are presented.