Challenges of and Learnings from Abandonment Operations in the Niger Delta

摘要

Abandonment of wells is a significant part of oilfield abandonment, accompanied by abandonment of facilities and installations. Well abandonment operations in the Niger Delta of Nigeria have covered different categories of wells; 1. Previously suspended wells. 2. Completed wells of varied completions design- single string, two string dual, two string multiple. 3. Wells with varying degree of vandalisation including cases where entire wellhead system were cut off and stolen. Long term safety and prevention of reservoir wellbore fluids, or gas from being released to the environment, is a top priority. While well abandonment is subject to detailed planning from the early design stages for a well, external circumstances throughout the well life may pose new needs or challenges that need to be factored in and addressed when approaching the actual abandonment. For vandalised wells, their condition makes sub-surface abandonment objectives difficult to achieve. Compliance to desirable permanent barrier isolation strategy and legislation becomes technically more challenging. Dual string wells with tubing hangers severed off are difficult to handle. In wells with high deviation, loss of tension on the tubing due to the severed hanger can cause a permanent buckling in deeper sections, making it impossible to run in tools. Wells completed in multiple zones are faced with the risk of inter-zonal communication in the case where pressure regimes are significantly different, which could lead to more complicated sub-surface challenges. This also creates the risk of having combined loss and kick situation from two different reservoirs respectively. The increasing severity of vandalisation has re-inforced these risks and has increased the cost of abandonment significantly. This paper highlights the challenges and learnings from an abandonment campaign in the Niger Delta. The unique experience of abandonment operations on vandalised wells is detailed. A focus on further potential cost savings game changers hinged on efficient execution, competitive scoping and leveraging on technology is discussed.