Performance Evaluation of CO₂ Soaking and Flooding Processes in Tight Oil Reservoirs

Abstract

CO 2 injection has been proven to be an effective method to improve oil recovery of tight oil reservoirs. CO 2 soaking and flooding are common processes used to constitute some CO 2 injection patterns. To investigate the difference of oil recovery performance and asphaltene precipitation distribution between CO 2 soaking and CO 2 flooding processes, CO 2 soaking and flooding tests under immiscible and miscible conditions were carried out with tight core samples. Then the NMR technique was utilized to analyze the microscopic remaining oil distribution and the asphaltene precipitation distribution after each test. The results indicated that the oil recovery in the small pores less than 0.6 μm was more influenced by the injection pressure, while the oil recovery in the large pores larger than 0.6 μm was more influenced by injection patterns. On the other hand, the asphaltene precipitation degree in different pores is usually relevant to oil recovery. In the large pores, the asphaltene precipitation degree of the soaking process was much lower than that of CO 2 flooding by 8.02 and 19.76% under immiscible and miscible conditions, respectively. In the small pores, the asphaltene precipitation degree of the soaking process was higher than that of CO 2 flooding by about 4%. Moreover, as injection pressure increased, the asphaltene precipitation caused by the soaking process was much less than that caused by CO 2 flooding. The results of the study can provide some theoretical support to determine a better CO 2 injection strategy for tight oil reservoirs with different characteristics.

Characterizing Residual Oil Distribution in Heavy Oil Reservoirs after Multiple Hot Water Huff and Puff: A Comprehensive Analysis

“…Additionally, Zhu et al found that residual oil is concentrated in clay micropores. Qian et al pointed out that huff and puff extraction is more effective than displacement methods in preventing asphaltene deposition in reservoirs. Huang et al investigated the deposition characteristics of asphaltenes and reservoir damage during the huff and puff process through NMR, noting that the precipitation rate of asphaltenes decreases with increasing huff and puff rounds.…”