Oil Rim Development: Mechanistic Study towards Optimal Exploitation

Abstract

Oil rims are categorized among marginal reservoirs characterized by challenging drive systems, unfavorable water and gas coning issues, and relatively high cost of development. Therefore, understanding the fluids dynamics and managing reservoir uncertainty are vital in such reservoirs. This paper presents the results of a comprehensive and systematic mechanistic study of an oil rim reservoir to determine the various factors that improve the oil recovery factor. The study includes the optimization of development strategies and the implementation of mitigation plans to reduce coning for a reservoir undergoing severe pressure drawdown. The reservoir has an oil thickness of 50 ft and is examined through four depletion scenarios. These scenarios are as follows: (1) the production of oil followed by gas, (2) the production of gas followed by oil, (3) the concurrent production of oil and gas, and (4) the production of gas only. A sensitivity analysis is performed on the pressure depletion values, pressure maintenance strategies, gas cap size, reservoir fluid type, reservoir heterogeneity, well orientation, and completion methods using Eclipse composition simulator. The development strategy applied limits unfavorable coning issues. Therefore improving the recovery factor from 9.8 % when producing the oil rim using vertical wells, to 30% when horizontal wells with smart completions. Results of the compositional simulation study show that the optimal development strategy (with the highest oil recovery factor of 45%) is the concurrent development of oil and gas by applying pressure maintenance using water injection at both the flank of the oil-water contact and the gas-oil contact. Moreover, the models show that using horizontal wells with smart completions is instrumental in reaching optimal recovery factors (above 30%), maintaining the reservoir pressure, and minimizing the cumulative water production, which enhances the economics of oil rim reservoirs, especially in the current volatile and low oil price era. To the best of our knowledge, this study is the first comprehensive attempt to thoroughly investigate oil rim reservoirs and identify opportunities to optimize their performance under different scenarios accounting for pertinent reservoir uncertainties and potential complex depletion history. The results presented in this paper will form clear guidelines for understanding and optimizing numerous oil rim reservoirs at different stages of maturity and development.