Productivity Enhancement and Optimization in High Sour Gas Field by Selective Stimulation through Post Perforation Dynamic Underbalance Technique and Production Logging

Abstract

XYZ, a marginal carbonate field in Western Offshore India was undertaken for development recently. During its exploration phase, around two decade ago, thick oil layer was discovered with high sour gas content (around 14000 ppm). The reservoir was delineated in small oil pool, where six wells were completed for production, including one water injector for pressure maintenance to support oil recovery. Production behavior of most of the wells had a unique response of rapid decline in short period of time with similar drastic loss in THP without any change in water cut. Production response of all these wells led the suspicion of near well bore skin development as the primary reason behind sharp decline in production. Acid treatment as a quick fix solution in carbonates was ruled out because of possible communication with bottom aquifer; coil tubing had multiple operational challenges in such a high H2S environment. Hence, to overcome the challenges and perform root cause analysis, it was planned to carry out the best possible set of data acquisition with rigless operations and plan ahead for productivity improvement and design future intervention as well. Production Logging, being an ideal diagnostic tool, was chosen to study the production profile and understand the reservoir and well behavior. Post analysis, a relatively new concept of selective stimulation with post perforation controlled dynamic underbalance technique was considered to be the best fit solution to address the skin and production decline problem in the field. The technique proved to be very beneficial and provided substantial increase in the wells production. The skin debris obtained in the process were analyzed to identify the cause of skin development and production plunge. Based on the results, further interventions were carried out in the well, which again proved to be very efficacious and increased the field production significantly. The paper has a detailed discussion on the root cause analysis and arriving to the appropriate solution for this kind of wells. It emphasizes on the importance of production logging prior to operation for better and successful planning and execution of the well intervention jobs leading to production gain. It also highlights the operational challenges in such hostile high H2S environment and the importance of planning and preparation to ensure safety of one and all.