Previous studies have shown that although supercritical CO₂ fracturing has prospects in the development of tight sandstone formations, there are relatively few related studies, and problems such as small sample size and insufficient quantitative analysis methods exist. Regarding tight sandstone, in this paper, 300 - mm cubic tight sandstone samples were used to conduct supercritical CO₂ fracturing experiments under true triaxial stress conditions. The experiment recorded the fluid pressure curves of hydraulic fracturing and supercritical CO₂ fracturing. By reconstructing the pre - space morphology of the induced fractures and using advanced algorithms to study the quantitative characteristics of the fracture surfaces, the spatial morphology and quantitative properties of water - induced fractures and supercritical CO₂ - induced fractures were compared, and the influence of in - situ stress on fracture propagation was discussed. The results show that: the time required for supercritical CO₂ fracturing is approximately 10 times that of hydraulic fracturing; under the same stress conditions, the breakdown pressure is nearly 25% lower than that of hydraulic fracturing; the fracture morphology caused by supercritical CO₂ fracturing is more complex; when the horizontal principal stress difference increases, the breakdown pressure value decreases, and the induced fracture morphology tends to be simplified; abnormal in - situ stress will increase the breakdown pressure and promote the development of more conductive fracture networks.
In the shale field, the supercritical CO₂ - shale interaction can incite adsorption - expansion during the short - term fracturing process, causing the existing natural fractures to close, which has an adverse impact on the hydrocarbon production rate after rock fracturing. Due to the high heterogeneity of shale, more research is needed to improve the understanding of the interaction between supercritical CO₂ and various minerals and organic matter in different types of shale and its controlling factors. Regarding the mechanism of CO₂ fracturing to enhance oil recovery, through a series of studies such as CO₂ fracturing experiments and numerical simulation studies, and by using nuclear magnetic resonance and computed tomography imaging technologies to carry out physical simulation experiments integrating fracturing - oil production, the relationship between fracture distribution characteristics and microscopic oil - gas distribution patterns has been elucidated. The results of physical experiments and numerical simulations show that for shale samples with different permeabilities, the CO₂ pre - fracturing method can effectively improve oil recovery, more fractures are generated in the CO₂ - injected section, and the production increases by 3 to 7 times. The mechanisms include crude oil modification, reservoir pressure increase, larger SRV (stimulated reservoir volume), and higher branch - fracture conductivity, among which the increase in branch - fracture permeability contributes the most to production.
Overall, the quantitative analysis of supercritical CO₂ fractures provides a key basis for in - depth understanding of its role in different formations; the short - term interaction with shale reveals its complexity in shale - gas development; the mechanism of CO₂ fracturing to enhance oil recovery provides a solid theoretical foundation for the practical application of this technology, which has important practical significance and fuel value for promoting the sustainable development of the energy field. In the future, further in - depth research is needed to better exert the advantages of supercritical CO₂ fracturing technology and make greater contributions to the efficient development and utilization of energy resources.