Analysis of the impact of CO2 injection on fracturing fluid flowback in shale gas wells

With the ongoing development of oil and gas resources, low-permeability tight reservoirs have become a focal point of research and technological innovation. To effectively address the challenges associated with fracture fluid retention, this study investigates the role of CO 2 in reservoir stimulation and productivity enhancement. The results reveal that liquid CO 2 induces a rapid temperature reduction in shale samples during the initial phase of injection with a temperature decrease of 16.1 °C observed within the first 10 min. However, the cooling rate diminishes significantly in the later stages, with only a 0.8 °C decrease recorded over the subsequent 10 min which indicating a distinct endothermic effect. The high diffusivity and low viscosity of CO 2 are key to its effectiveness in enhancing reservoir pressure and improving fracture conductivity. Additionally, the expansion-induced cooling effect of CO 2 lowers wellbore temperatures, thereby lowering the viscosity of the fracturing fluid and improving its mobility. A stable pressure gradient provides the driving force for efficient fracture fluid recovery, which significantly boosting recovery efficiency and productivity. The results further indicate that at injection rates of 5000 m 3 /d, 10,000 m 3 /d, and 15,000 m 3 /d, the recovery volumes are 97%, 96%, and 88% higher than those achieved with water-based fracturing fluids, respectively. These findings demonstrate the significant advantages of CO 2 injection in increasing reservoir pressure and promotes the flow of oil and gas at the well bottom. The promising application potential of CO 2 in low-permeability tight reservoirs underscores its value as an innovative approach to reservoir stimulation and productivity optimization. This study provides the first comprehensive analysis of CO 2 's dual role in enhancing flowback efficiency through thermal, mechanical, and fluid dynamic interactions, offering a paradigm shift from conventional water-based fracturing.