Oil production performance and reservoir damage distribution of miscible CO2 soaking-alternating-gas (CO2-SAG) flooding in low permeability heterogeneous sandstone reservoirs

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

“…When pore size was larger than 0.6 μm, the displacement effect of the flooding process could result in the oil recovery of CO 2 flooding 30% higher than that of the CO 2 soaking process. On the other hand, whether under a miscible or immiscible condition, the soaking process not only can delay gas channeling 6 but also can improve the oil recovery in small pores by about 7% compared with CO 2 flooding (Figure 9). Therefore, for the tight matrix with a high proportion of small pores, it is beneficial to improve oil recovery through adding a soaking period during CO 2 injection.…”

“…5 There are several CO 2 injection−production patterns that are often used in the field to implement CO 2 injection, such as CO 2 flooding, CO 2 huff-and-puff, CO 2 soaking-alternating-gas flooding. 6 Different injection patterns have different emphases. Commonly, CO 2 soaking process and CO 2 flooding process are essential processes to constitute these CO 2 injection−production patterns.…”

“…However, in tight oil reservoirs, the diffusion effect plays an important role . There are several CO 2 injection–production patterns that are often used in the field to implement CO 2 injection, such as CO 2 flooding, CO 2 huff-and-puff, CO 2 soaking-alternating-gas flooding . Different injection patterns have different emphases.…”

Oil production enhancement, asphaltene precipitation and permeability damage during CO2-SAG flooding of multi-layer sandstone reservoirs

“…The CO2-soaking-alternating-gas flooding process (CO2-SAG) is a combination of conventional continuous miscible CO2 flooding with a CO2 soaking stage from the CO2 huffand-puff process [10] . In the first stage CO2 is continuously injected into the reservoir in the same way as in the conventional miscible CO2 process.…”

“…We have carried out SAG flooding experiments on cores with similar permeability but different pore throat structures and single heterogeneous long cores, and studied the effects of pore structure and linear heterogeneity on the micro and macro crude oil production improvement of CO2-SAG flooding and the distribution of permeability damage [10,13] . Furthermore, there has been no previous study of the combined improvement in hydrocarbon recovery and progress of permeability damage in heterogeneous reservoirs consisting of multiple layers of rocks with different pore microstructures after both types of flooding.…”