Experimental Study and Performance Investigation of Miscible Water-Alternating-CO2 Flooding for Enhancing Oil Recovery in the Sarvak Formation

This experimental study is aimed at evaluating the performance of the miscible Water-Alternating-CO2 (CO2-WAG) flooding as a function of slug size and WAG ratio based on the ultimate oil recovery in the Sarvak formation. In this research, initially the slim-tube apparatus was used to determine the Minimum Miscibility Pressure (MMP) of the Sarvak heavy oil and CO2 at the constant reservoir temperature. Then, a total of seven core flooding experiments were performed by using the sandstone core samples collected from the Sarvak formation. These experiments were conducted through respective water flooding, miscible continuous CO2 flooding, and miscible CO2-WAG flooding. In the miscible CO2-WAG flooding, different WAG slug sizes of 0.15, 0.25, and 0.50 Pore Volume (PV) and different WAG ratios of 1: 1, 2: 1, and 1: 2 were applied to investigate their effects on the oil Recovery Factor (RF) in the Sarvak formation. The results showed that, in general, the miscible CO2 Enhanced Oil Recovery (CO2-EOR) process is capable of mobilizing the heavy oil and achieving a high and significant oil RF in the Sarvak formation. The miscible CO2-WAG flooding has the highest oil RF (84.3%) in comparison with water flooding (37.7%), and miscible continuous CO2 flooding (61.5%). In addition, using a smaller WAG slug size for miscible CO2-WAG flooding leads to a higher oil RF. The optimum WAG ratio of the miscible CO2-WAG flooding for the Sarvak formation is approximately 2: 1. The results also demonstrated that, more than 50% of the heavy oil is produced in the first two cycles of the miscible CO2-WAG flooding. The optimum miscible CO2-WAG flooding has a much less CO2 consumption than the miscible continuous CO2 flooding.