Rigless Abandonment Strategy for Deepwater Field – Case Study for Bonga End of Field Life

Abstract In the last two decades, exploration and development of oil and gas in the deepwater environment have increased significantly, resulting in a larger number of subsea wells globally. Consequently, the abandonment of major oil and gas fields is becoming frequent as aging fields reach the end of their productive and economic limits. The impact of these abandonments presents significant challenges for the oil and gas industry. The rig cost accounts for about 40% to 50% of the total expenditure of rig-based well abandonment operations in Deepwater due to high day rates. The challenge for the oil and gas industry is to execute well abandonment scope efficiently using novel tools and technologies to guard against escalations and reduce well abandonment costs. This is important because well abandonment projects require significant investment with no financial return. The objective of this paper is to present an efficient and cost-effective Rigless abandonment strategy that meets the industry requirements. Rigless plug and abandonment strategy for Deepwater oil and gas fields transfers the well abandonment execution scope from the conventional rig-based solution to an appropriately equipped well intervention vessel, which presents opportunity to optimize the subsea well abandonment process and reduce subsea well abandonment cost through the utilization of lower cost unit. This paper presents a review of well intervention vessels and applications, well abandonment fundamentals and standards, Rigless abandonment strategy, and industry best practices in the Deepwater environment. A case study using the Bonga Deepwater field is presented, followed by a review of the field, well design, and a selected candidate well to assess the well's suitability for rigless abandonment. As part of the company's journey towards full Rigless well abandonment in the Bonga Deepwater field, the leanings and knowledge gained from previous Rigless well intervention activities and well abandonment in the Bonga field were used to design a fit-for-purpose and cost-effective Rigless abandonment for subsea well. The case study demonstrates the feasibility and significant reduction in Abandonment Expenditure (ABEX) per well by approximately 40% compared to the rig-based approach. This outcome presents a huge opportunity to reduce well abandonment liability provision and free up cash for other projects and new investments.