Influence of CO2–water–rock interactions on the fracture properties of sandstone from the Triassic Xujiahe Formation, Sichuan Basin

Abstract

Carbon dioxide (CO2) storage in deep saline aquifers has been lauded as one of the most effective techniques to mitigate greenhouse effects globally. Nevertheless, despite many investigations, clarifying the influence of CO2–water–rock interactions on the fracture characteristics of sandstone remains a challenge. In this work, the fracture properties of sandstone collected from the Triassic Xujiahe Formation are systematically studied in tests simulating CO2 sequestration. The results indicate that the water–rock interactions occur in a system of sandstone and CO2 solution. Due to the interactions, the porosity of sandstone specimens slightly increases from 8.24 to 8.45% when immersed in CO2 solution and from 8.20 to 8.40% in pure water after 28 days. In addition, the parameters of fracture toughness, tensile strength, uniaxial compressive strength and elastic modulus are reduced by 24.12%, 27.16%, 31.78% and 33.21% after immersion in pure water, while they are reduced by 24.05%, 29.72%, 30.75% and 25.79% after immersion in CO2 solution, respectively. These results suggest that the mechanical properties of the Xujiahe sandstone deteriorate after soaking. The results also show that the critical fracture energy of sandstone specimens after immersion in the CO2 solution is 10.4% lower than that in pure water and 24.1% lower than that under natural drying conditions. These research results have great significance for understanding the dissolution processes during CO2 sequestration and their influence on the fracture properties of sandstone, which may be theoretically instructive for CO2 storage in the Xujiahe Formation in the Sichuan Basin.