A sandstone reservoir at a depth of 2800 m in a western India onshore field contains highly under saturated light oil of 470 API with viscosity of 0.2 cp. The reservoir has a permeability ranging 50 to 300 md and high temperature of around 130 Deg C. It is exploited by supplementing the partial water drive with water injection. Water injection was initiated in the early part of its producing life and has recovered more than 30% of OIIP. Meanwhile, availability of natural gas from deeper reservoirs in the field initiated a thinking process to examine the processes involving both miscible and immiscible displacement with gas injection to improve the recovery factor from the reservoir. The reservoir was not found suitable for miscible process due to higher miscibility pressure as compared to prevailing reservoir pressure of 250 Kg/cm2. Viability of immiscible WAG was ascertained through both laboratory investigations and numerical simulation prior to its testing on a pilot scale in the field. The process resulted in an increase in oil production along with reduction in water cut from the pilot and offset wells. Encouraging pilot results led to the decision of expanding the process to the entire field. The paper also evaluates the effects of different critical parameters on the recovery factor from immiscible WAG process through reservoir simulation studies.

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.

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The ONGC operated XYZ field is the farthest oilfield from shore located in western offshore of India. Based on the remoteness and marginal nature of the field, it was developed by deploying an Early Production System and brought on production in 2006. Concurrent exploration and development activities resulted in horizontal & vertical growth of the field, nearly doubling the in-place reserves. Subsequently, the field development strategies were revised and the Early Production System was replaced with FPSO in 2013. Post FPSO installation, back pressure in the field increased leading to sub-optimal production from the self-flowing wells necessitating early installation of artificial lift. The reservoir is multi-layered limestone in a depth span of 2100–2850m. Reservoir pressure is almost hydrostatic and temperature ranges from 120–140°C. The crude is light and highly under saturated with bubble point pressure less than 100 kg/cm2. With low production GOR (~40 v/v) and no nearby source of gas, possibility of using gas lift was eliminated. However, highly under saturated crude with favourable reservoir conditions made it an attractive proposition to install ESP as artificial lift in the field. ESP installation campaign kicked off in May-13. The campaign suffered initial setbacks in the form of premature/frequent ESP failures resulting in production downtime. Completion of the new wells with predesigned ESP since inception led to sub-optimal production performance of some wells. The early ESP failures warranted a comprehensive review of ESP design and installation strategies followed in the field. Accordingly, accelerated mid-course corrections were made and new strategies were formulated for optimized ESP design. ESP installation methodologies were also reviewed to minimize operational hiccups. This was followed by close monitoring of ESP performance for further optimization opportunities in accordance with dynamic reservoir conditions. The performance of ESPs designed and installed using revised methodology was in line with the expectations. With improved ESP design and installation practices, sustained production could be realized and the field witnessed turnaround in production with peak oil rate of 32000 bopd through 28 wells in Feb-15. The paper discusses lessons learnt while overcoming the challenges and procedures implemented in design, installation, operation and monitoring of ESPs in XYZ field which led to a successful endeavor to revive the field to its anticipated potential.