Bonga Deepwater Project Mid-Life Abandonment Campaign – A Success Story

Abstract When oil and gas wells have been produced to the end of useful life, when the cost of production relative to the value derived converge to a point when producing the well is no longer profitable, the wells are decommissioned. Oil and gas well decommissioning and restoration refers to the process of permanently sealing and abandoning oil and gas producing reservoirs within a wellbore that are no longer productive or economical to operate, in a way that ensures safety and environmental protection in accordance with industry and local regulatory standards and requirements. As part of this philosophy, The project strategy was to decommission and abandon depleted wells as they reach their end of useful life in accordance with Shell PLC guidelines and local regulation as specified in Environmental Guidelines and Standards for the Petroleum Industry In Nigeria (EGASPIN). The field's midlife abandonment project was a first in deep water environment in Nigeria, developed and executed to permanently abandon selected wells that have reached their end of useful life by permanently isolating the reservoirs zones that are capable of flow and restoring caprock. This was achieved by recovering the completion, production and intermediate casing strings to expose the reservoirs traversed by the wellbore, then restoring the caprock using cement plugs which were set to create a rock-to-rock isolation of all zones with flow potential within the primary wellbore. The objective was to prevent crossflow between reservoir zones, isolate the reservoirs from the environment and marine life while safeguarding all subsea infrastructure from damage arising from the well abandonment operations. In total, thirteen wells with varying degrees of complexity were successfully decommissioned and restored without incidents or accidents. The fourteenth well had to be re-suspended due to multiple complex challenges which emerged during the abandonment campaign. The well needed to be replanned, ensuring the required equipment to execute the emerging challenges were available. As with every new project, several challenges were encountered, and new ideas were developed. These ideas include achieving better well integrity coupled with improved tubing and casing recovery practices and optimized cement plug placement will be a foundation for future deep water well abandonment in Nigeria specifically and the industry at large. The learnings from the project were adopted to generate a Standard Operating Procedure (SOP) for deep water well abandonment. These SOPs and all other learnings and best practices that led to the success of the mid-life abandonment campaign will be adopted in executing the end of field life abandonment for the project and will be shared on this paper.