Unlocking the Potential of a Giant Carbonate Reservoir: Optimizing Oil Recovery in Tight Zones Following a Long Period of Gas Injection Development

Abstract Recurring evaluation of the selective completion and development strategy of individual reservoirs is crucial to ensure optimal performance. This paper presents a new approach for optimizing the injection scheme in highly communicated reservoirs. After a long period of gas injection in the subject reservoir, gas percolation to the overlying reservoir becomes critical. This paper aims to propose a plan that can enhance the recovery of the subject reservoir without compromising other reservoirs’ performance. A full-field reservoir simulation model, in integration with surveillance data, including a tracer study were used to investigate various development scenarios, including additional wells, artificial lift need, voidage replacement ratio, balance between peripheral and pattern water injection, and the optimum target injection rates. After each scenario, it was observed that the predominant heterogeneities caused a large amount of oil to be left behind. Therefore, this paper also demonstrates a method for locating and quantifying the remaining oil and determining the best techniques for its recovery. The optimized scenario resulted in an extended plateau and an increased recovery. The results demonstrated the benefits of switching from gas injection to water injection in the parts of the reservoir where water injection was feasible. The extreme north of the reservoir where water can’t be injected without fracturing, has insignificant remaining oil after long time of gas injection. The gas injectors in this part of the reservoir are sidetracked within the reservoir and switched to water injectors. These actions reduced the gas percolation to the upper reservoir, increased the ultimate recovery, and enhanced the economics significantly due to the lower operating cost. The new development plan of the subject reservoir showed the importance of thoroughly evaluating and integrating all the available data and connecting these data with the reservoir geology to better position the new wells. The updated development plan led to extension of the production plateau resulting in additional recovery and improved economics. This paper highlights the importance of optimizing the injection scheme for the target and neighboring reservoirs. It highlights that relying solely on common development options does not recover the remaining oil effectively. To enhance recovery, the paper presents a method for quantifying and targeting the remaining oil to select the most suitable recovery technique.