Mitigating Well Integrity Challenges of Vintage Wells: A Case Study from Mumbai Offshore Field

Abstract Vintage wells, characterized by their age, often present structural integrity challenges, necessitating specialized approaches to ensure their safety and longevity. In Mumbai’s offshore region, the operator oversees over 250 wellhead platforms, the majority of which are more than 25 years old. Given the high demand for increased recovery factors and production rates, a comprehensive well rehabilitation strategy was imperative. Prior to the rig deployment, based on various comprehensive assessments, found that surface casing parted below the wellhead in five specific wells due to severe corrosion. In light of the findings, all wellheads, 30" conductor casings, 20" surface casings, and in a few cases, the 13 3/8" intermediate casings were replaced, specifically from the boat landing deck. The onset of the monsoon season was an additional challenge faced by this project. With the help of pre job analysis, planning and the on-site execution, the integrity of the five wells has been reinstated. It helped in avoiding the abandonment of existing wells, slot recovery activities like changing the entire conductor and surface casings and further drilling of new wells with different directional trajectories. The uncertainties faced are controlling gas bubbling from the annulus of 9 5/8" (production casing) - 13 3/8" (intermediate casing) in one of the wells and requirement of changing intermediate casing (13 3/8") in another well. The method of carrying out the casing replacement activity from the boat landing deck was implemented in consideration with prevailing oil and gas standards and procedures. Thereby, the three water injector wells are serving their intended purpose by contributing to the improvement of reservoir pressure, while the two oil producer wells are enhancing oil exploitation from the carbonate reservoir. The implementation of innovative methods, comprehensive risk analyses, and stringent safety precautions contributed to the timely and efficient completion of the project, ultimately enhancing reservoir pressure and augmenting oil production from the carbonated reservoir. This paper provides a detailed account of the methodology, pre-job planning for casing repair and wellhead replacement, on-site execution, successful completion of the well restoration process, and the precautionary initiatives to address possible casing integrity issues in the future.