Subsea well intervention challenges, OML 126 Wells – A Case Study

Abstract With the recent decline in price of crude, more cost effective ways are explored to ensure that the production rates are sustained and increased. The need for cost effective subsea well intervention has been discussed and documented over the last few years. The increasing number of installed subsea wells combined with the increasing age of subsea fields continues to drive demand for more efficient subsea well intervention. Traditionally the accessibility to subsea wells is considered more difficult and represents a large cost compared to wells with direct platform access. Even minor jobs represent large expenses, leaving a gap between intervention frequency on subsea wells and wells with direct platform access. The average recovery rate for a subsea well is considerably lower than that of a comparable surface well due to the relatively more complicated well intervention and maintenance issues. Using heavy and traditional rigs for subsea intervention is costly and time consuming due to the high day-rates and mobilization aspects. The base costs are therefore considerable higher as compared to surface well intervention where tools can be deployed directly through the risers from the production unit. At Addax Petroleum, Nigeria, the re-entry and intervention of existing poor producing subsea wells was identified as a cost effective method to maintaining production in the reasonably high cost oil subsea environment. However the major challenge with subsea intervention is the uncertainty that surrounds the planning and operations which grows exponentially with the age of the well. As factors like corrosion, and well integrity (cement and casing) all become critical in the successful delivery of the well. The availability of required service equipment and modes of operation also become very critical especially for old and obsolete Subsea equipment. There is always a significant extra cost spent if any of the identified or unidentified risks manifest. In 2014 Addax Petroleum embarked on a successful re-entry campaign as part of the second phase of its Okwori Field Development Plan. This paper highlights on the lessons learned from the campaign, discussing the challenges, planning, and execution phases of the successful well re-entry campaign in deep water operations.