Experimental study of influence of CO₂ treatment on fracture toughness of tight sandstone

A large amount of CO2 will be emitted after the burning of fossil fuels, causing global warming and glacier melting which will bring a huge threat to the living environment. Atmospheric clearance through the capture, utilization or storage of CO2 is one of the technologies for dealing with global climate change. In order clarify the mechanization of supercritical CO2 fracturing, the tight sandstone cores in the Jinqiu Gas field, Sichuan Basin were used to carry out the effect research of supercritical CO2 on fracture toughness. The results show that after the treatment of tight sandstone on supercritical CO2, the degradation degree of I-type fracture toughness decreases by 23.6%-33.6% when the soaking days reach 15 days. At the same reaction time, the fracture toughness under 20 MPa and 60 degrees C is lower by 3 similar to 11% than that under 10 MPa and 50 degrees C. Meanwhile, the geometric fracture trajectories of sandstone samples before and after the treatment of supercritical CO2 treatment are observed. Before the treatment, the S-max was 1.46 mm and the fracture angle was 10.24 degrees, but after the treatment, the parameters were 0.93 mm and 3.41 degrees, respectively. The fracture trajectories after multiple polishing were observed by SEM imaging, which shows that the fractures can propagate directly through the mineral particles after the supercritical CO2 treatment, which causes the transcrystalline fracture. It is conducive to initiating, propagating, and destroying I-type fractures under smaller external loads. The results further improve the mechanism of CO2 on fracture toughness of tight sandstone, which is useful to explore the feasibility of CO2 fracturing of low-pressure tight sandstone, and provide theoretical support for the safety of CO2 fracturing and CO2 geological sequestration of tight sandstone.