Fracture Pattern and Energy Release on a Simulated Acid-Etched Fault and Implications for CO2 Geological Storage Induced Seismicity

Abstract Although CO 2 geological storage (CGS) is an effective way to reduce CO 2 emissions to the atmosphere, the acidic environment caused by CO 2 injection can potentially induce fault rupture and seismicity. To simulate fault rupture under acid etching, multi-stage shear tests were conducted on acid-treated basalt samples at shear rates of 0.5, 0.75, and 1 mm/s using a custom-designed apparatus under constant normal stiffness (CNS) conditions. High-speed imaging was employed during the shear process to capture real-time deformation, whereas 3D surface scanning and X-ray computed tomography (CT) were conducted post-shearing to quantify the alterations in surface morphology and internal structure. Experimental results reveal that the samples are more prone to fracture with increasing acid etching duration and shear rate. The sudden drop in shear stress is a hallmark of fracturing or induced seismicity, and the shear strain energy stored within the sample is the source of this event. Additionally, a formula for calculating fracture energy is proposed. Acid etching modifies the fracture propagation path primarily by weakening interparticle bonds, rather than dissolving entire particles. This promotes fracture initiation at severely worn regions and facilitates propagation along particle contacts and grain boundaries. This study provides valuable references for the reasonable monitoring and magnitude prediction of seismic events during the CGS process, thereby enhancing storage efficiency and safety.