Experimental study on the fracture behavior of sandstone after ScCO2–water–rock interaction

Geological sequestration of carbon dioxide is one way of offsetting carbon emissions. During geological CO2 sequestration, any effects that CO2 may have on the physical and mechanical properties of the caprock can potentially affect the stability of its storage. This paper investigates the fracturing behavior of sandstone immersed in water dissoluted with supercritical carbon dioxide (ScCO2). For this purpose, the fracture toughness of sandstone was tested after different durations of immersion in water with ScCO2 (10 days, 20 days and 30 days). Furthermore, the surface and fracture characteristics of the sandstone were evaluated with X-ray diffraction (XRD), X-ray fluorescence (XRF), and scanning electron microscopy (SEM). The results show that: (1) The mode I fracture toughness (KIC) of sandstone reduced by up to 23.91%, 20.43%, and 31.92% after immersion in water with ScCO2 for 10 days, 20 days and 30 days, respectively, indicating clear temporal heterogeneity in the damage caused to sandstone by ScCO2 and water. (2) Similar variation occurs in the maximum deviation distance of sandstone failure cracks with an increase in saturation time as in fracture toughness (KIC); that is, the maximum deviation distance increases in parallel with fracture toughness. (3) ScCO2–water–rock interactions change the mineral composition of sandstone. As a result, many pores and cracks appear in the sandstone, especially after 30-day saturation, seriously damaging its structure; this is the direct cause of the decrease in the ability of the sandstone to resist fracture. The results of this study provide a significant theoretical reference for evaluating the long-term stability of geological CO2 sequestration under caprock.