Supercritical CO ₂ Seepage Characteristics in Fractured Tight Sandstone: Effects of Confining Pressure, Temperature, and Fracture Morphology

Achieving efficient injection and long-term secure storage in deep tight reservoirs remains a critical scientific challenge for supercritical CO2 (ScCO2) geological utilization and carbon reduction strategies. Previous studies on fracture seepage are often limited to single factors or idealized models, making it difficult to reveal the intrinsic roles of temperature–pressure coupling and fracture geometry in realistic reservoirs, particularly lacking systematic comparison of fractures with different origins. This study investigates tight sandstone from the Jurassic Shaximiao Formation in the Sichuan Basin, using two fracture types─ScCO2-fractured and Brazilian-split─subjected to seepage experiments under simulated reservoir temperature and confining pressure. By combining three-dimensional (3D) point-cloud scanning to quantify surface morphology parameters (Sa, Sq, Sz, D, and JRC), the study innovatively integrates fracture generation, seepage testing, and 3D fracture characterization, providing the first systematic comparison of ScCO2 flow in two fracture types. Results indicate that confining pressure suppresses permeability (5.9–24.3% decrease per 5 MPa), with greater sensitivity at lower temperatures. Temperature exerts a significantly stronger inhibitory effect on permeability than confining pressure (32.2–48.2% decrease per 20 °C), reflecting the coupled impacts of fluid properties, thermal expansion, and mineral reactions. Comparative analysis further reveals that ScCO2-induced fractures display a distinctive “macroscopically rough–microscopically smooth” multiscale feature: Sa/Sq/Sz are 90.8–125.5% higher than in Brazilian fractures, while fractal dimension decreases by ∼4.7%, challenging the conventional assumption that roughness and complexity are positively correlated. This structure confers higher permeability but reduced stability. Conceptual flow evolution diagrams illustrate the staged migration and path-splitting behavior of fluid within fracture networks, providing new insights into complex fracture flow. These findings offer theoretical guidance and engineering implications for enhanced production in tight reservoirs, CO2 storage security, and subsurface energy utilization under carbon neutrality.