Impact of proper design of operating parameters on the performance of CO2-Water Alternating Gas (CO2-WAG) injection: a simulation study

Abstract

Water-alternating-gas (WAG) is one of the enhanced oil recovery (EOR) methods in which both water and gas are injected into the reservoir. Among different WAG processes, CO2-WAG is one the most environmental-friendly and efficient methods. The low minimum miscibility pressure (MMP) of CO2 turns this gas to a special candidate for EOR applications. In this study, impact of anisotropy coefficient and operating parameters including injection rate, pattern size and slug size on performance of this process was investigated through 360 different cases of numerical simulation. Also, a modification to the currently used dimensionless aspect ratio was proposed to enhance the accuracy of predicting oil recovery factor during WAG process. Generally, it was concluded that regardless of anisotropy coefficient, oil recovery factor increases as the ratio of well distance to reservoir thickness increases. For instance, for anisotropy coefficient of 0.1, the average recovery factor for well distance to reservoir thickness of 10 and 100 was 68% and 74%, respectively. In addition, it was concluded that the performance of WAG process is logarithmically correlated with anisotropy coefficient and well distance to reservoir thickness. Finally, it was concluded that the proposed modification for the dimensionless aspect ratio considerably increases its accuracy.