Stimulation of tight basalt reservoirs using supercritical carbon dioxide: Implications for large-scale carbon sequestration

Although supercritical carbon dioxide (SC-CO 2 ) fracturing shows tremendous potential for maximizing injection efficiency and enhancing storage volumes, few investigations have been reported on the SC-CO 2 fracturing characteristics of tight basalts and the reactions between fractured basalt and SC-CO 2 . In this study, hydraulic fracturing experiments were conducted on cylindrical basalt specimens using water and SC-CO 2 as fracturing fluids. Geometric parameters were proposed to characterize the fracture morphologies based on the three-dimensional (3D) reconstructions of fracture networks. The rock slices with induced fractures after SC-CO 2 fracturing were then processed for fluid (deionized water/SC-CO 2 )-basalt reaction tests. The experimental results demonstrate that SC-CO 2 fracturing can induce complex and tortuous fractures with spatially dispersed morphologies. Other fracturing behaviors accompanying the acoustic emission (AE) signals and pump pressure changes show that the AE activity responds almost simultaneously to variation in the pump pressure. The fractured basalt blocks exposed to both SC-CO 2 and water exhibit rough and uneven surfaces, along with decreased intensities in the element peaks, indicating that solubility trapping predominantly occurs during the early injection stage. The above findings provide a laboratory research basis for understanding the fracturing and sequestration issues related to effective CO 2 utilization.