Stimulation and Sequestration Mechanism of CO(2) Waterless Fracturing for Continental Tight Oil Reservoirs

[Image: see text] CO(2) fracturing is a promising technology for oil field development in tight, continental deposits, with potential advantages of enhanced oil recovery (EOR), CO(2) sequestration, and water conservation. Compared with CO(2)-EOR techniques, such as CO(2) huff and puff and CO(2) flooding, CO(2) can interact with reservoir rock and fluid under higher pressure conditions during fracturing, resulting in CO(2) stimulation and sequestration effects that differ from those that occur during conventional CO(2)-EOR. In this paper, the CO(2) interactions between CO(2) and reservoirs in continental tight oil reservoirs under fracturing conditions are systematically studied through laboratory experiments. The results show that under high pressure, CO(2) effectively changes the pore structure through the extraction of hydrocarbons, dissolution of the rock matrix, and migration of minerals. CO(2) dissolution of the rock matrix can significantly increase the number and complexity of fractures. Furthermore, CO(2) has a higher solubility in formation fluid under high-pressure conditions. Given the higher pressures, CO(2) forms a miscible phase with crude oil, diffuses more deeply into the formation, and reacts fully with the reservoir minerals and fluid during CO(2) fracturing. Accordingly, CO(2) can improve the permeability of the reservoir and flowability of crude oil significantly. Hence, CO(2) fracturing can enhance oil recovery and CO(2) sequestration more effectively. Core displacement experiments indicate that oil recovery of CO(2) soaking process after CO(2) fracturing is 36%, which is 12% and 9% higher than those of CO(2) huff and puff and CO(2) flooding with 5 pore volume, respectively. Field tests show that average oil production after CO(2) fracturing is 1.42 times higher than that after CO(2) flooding, which further validates the advantage of CO(2) fracturing and demonstrates its huge application potential.