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 CO2 in reservoir stimulation and productivity enhancement. The results reveal that liquid CO2 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 CO2 are key to its effectiveness in enhancing reservoir pressure and improving fracture conductivity. Additionally, the expansion-induced cooling effect of CO2 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 m3/d, 10,000 m3/d, and 15,000 m3/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 CO2 injection in increasing reservoir pressure and promotes the flow of oil and gas at the well bottom. The promising application potential of CO2 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 CO2's dual role in enhancing flowback efficiency through thermal, mechanical, and fluid dynamic interactions, offering a paradigm shift from conventional water-based fracturing.