Quantitative insight into fracture distribution during supercritical CO2 fracturing in tight sandstone formation

Supercritical CO₂ (SC-CO₂) fracturing stands out a promising waterless stimulation technique in the development of unconventional resources. While numerous studies have delved into the induced-fracture mechanism of SC-CO₂, the small scale of rock samples and synthetic materials used in many studies have limited a comprehensive understanding of fracture propagation in unconventional formations. In this study, cubic tight sandstone samples with dimensions of 300 mm were employed to conduct SC-CO₂ fracturing experiments under true-triaxial stress conditions. The spatial morphology and quantitative attributes of fracture induced by water and SC-CO₂ fracturing were compared, while the impact of in-situ stress on fracture propagation was also investigated. The results indicate that the SC-CO₂ fracturing takes approximately ten times longer than water fracturing. Furthermore, under identical stress condition, the breakdown pressure (BP) for SC-CO₂ fracturing is nearly 25% lower than that for water fracturing. A quantitative analysis of fracture morphology reveals that water fracturing typically produces relatively simple fracture pattern, with the primary fracture distribution predominantly controlled by bedding planes. In contrast, SC-CO₂ fracturing results in a more complex fracture morphology. As the differential of horizontal principal stress increases, the BP for SC-CO₂ fractured rock exhibits a downward trend, and the induced fracture morphology becomes more simplified. Moreover, the presence of abnormal in-situ stress leads to a further increase in the BP for SC-CO₂ fracturing, simultaneously enhancing the development of a more conductive fracture network. These findings provide critical insights into the efficiency and behavior of SC-CO₂ fracturing in comparison to traditional water-based fracturing, offering valuable implication for its potential applications in unconventional reservoirs.