Subsea Well Intervention – An Operator's Experience in First Deepwater Temporary Wells Suspension in West Africa

Abandonment and decommissioning activities of oil and gas assets had been on the increasing trend for the past few years. Mature assets approaching end of life cycle and depleted production coupled with the low oil price environment has contributed to poor economic evaluation of the producing fields. This paper will discuss operator's experience in planning and executing subsea well intervention to temporary suspend fifteen (15) deepwater subsea wells tied to a Floating Production, Storage and Offloading (FPSO) unit in West Africa. The approach of the temporary wells suspension will be shared. Decision to temporary suspend the wells was made to meet the objective of releasing the FPSO early due to high operating cost. This temporary wells suspension design is mainly driven by the objective to meet the industry standard and best practices in re-instating double barrier envelope in the wells during the suspension period. During the planning stage few methods of barrier installation including contingency plans were considered. The temporary barriers placement were designed with end state in mind, the subsequent wells plug and abandonment after the suspension period. Based on the barriers placement philosophy, the subsea well intervention activities were planned and followed by the selection of vessel or rig for the operations. Drivers behind the temporary wells suspension design, approach for subsea well intervention - using riser based or riserless operations; and selection of vessel or rig for the operations will be shared in this paper. In addition, the lessons learnt and optimization opportunity throughout the execution of this subsea well intervention activity will be presented. This project is the pioneer to deepwater subsea abandonment and decommissioning (A&D) in the region of West Africa. The fifteen deepwater subsea wells were successfully suspended safely, ahead of planned schedule and below AFE cost. The lessons learnt from successful temporary wells suspension through subsea well intervention carried out by operator is believed to benefit all industry players, including the regulators, operators, service partners; and could be reference for industry's deepwater subsea decommissioning.