A Systematic Approach in Methodology for Permanent Plug Placement in Deepwater Subsea Plug and Abandonment Campaign

Wells plug & abandonment was carried out in a deepwater field (Field C) offshore West Africa. There were 15 deepwater subsea wells, in this field. Thirteen of the wells were completed with Open Water Vertical Xmas Tree (OXT) while remaining two were completed with Enhanced Vertical Xmas Tree (EVXT). All the wells were permanently abandoned with permanent barriers established in accordance to Norsok D-010, rev 4. (2013). This involved establishing well barriers which would both horizontally and vertically effective. Plug and abandonment in a subsea environment remains a major challenge most operators face around the world. This paper will discuss the systematic approach to establish the methodology for plug placement by Operator for installing permanent abandonment barriers in their campaign. The paper shall discuss the systematic approach in permanent plug placement as well as highlight challenges and lessons learnts. The paper discusses the guidelines and philosophy to devise methodology for permanent plug placement based on industry capability. The paper also shares the novel approach in devising Plug Placement decision tree as well as well as explanation on principle behind the method. The paper will share on the process flow used by Operator for the permanent abandonment of these wells. Other than that, paper shall highlight the implementation of the decision tree during operations with examples. The best practices and lessons learnts in the plug placement methodology implementation during Operator's campaign in subsea plug and abandonment shall also be discussed in this paper. Ultimately, the paper shall also share on the recommendation for future subsea abandonment planning to assist Operator in their planning.