The Mechanisms and Applications of CO 2 -Elevated Fracturing in Tight Sandstone Gas Reservoirs: A Comprehensive Investigation for Enhanced Oil and Gas Recovery

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Abstract
This study systematically investigates the mechanisms and field applications of pre-CO2-energized fracturing in normal-pressure tight sandstone gas reservoirs in western Sichuan, aiming to overcome challenges such as insufficient flowback energy, rapid pressure depletion, water-lock damage, and the limited applicability of conventional fracturing technologies. Using a comprehensive approach integrating laboratory experiments, theoretical analysis, and field trials, the interactions among CO2, formation water, the rock matrix, and the fracturing fluids were thoroughly examined. Experimental results demonstrate that CO2-water-rock reactions significantly improve reservoir properties, increasing core permeability by 43.38%–61.73% and porosity by approximately 9%, thereby enhancing seepage capacity. Preinjection of CO2 was found to reduce fracture initiation pressure by 29.48% and promotes the development of more complex fracture networks. In addition, CO2 accelerates gel breaking of fracturing fluids and enhances flowback efficiency, effectively mitigating formation damage. Competitive adsorption experiments further demonstrate that CO2 exhibits 1–4 times higher adsorption capacity than CH4, which is beneficial for both methane displacement and CO2 sequestration. Field applications in Wells MP87-1 and SL101 achieved substantial improvements in flowback rate and production performance, with stable gas production significantly exceeding geological expectations. These results verify that pre-CO2 energized fracturing is an effective and environmentally beneficial stimulation technology capable of enhancing recovery while achieving CO2 geological sequestration.

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