An Experimental Study on the Influence of CO2 Real-Time Contact on the Mechanical Properties of Shale

The influence of CO2 on the mechanical properties of shale is one of the key factors to consider for enhancing shale oil and gas exploitation and realizing CO2 geological storage. In this paper, triaxial mechanical experiments of rock under real-time contact with CO2 under different conditions were carried out for the Chang 7 shale of the Yanchang Formation in the Ordos Basin. The results show that under the influence of real-time contact with CO2, the triaxial compressive strength of shale decreases with an average decrease of 3.77% and a maximum decrease of 6.58% under the experimental conditions. The elastic modulus increased with an average increase of 8.54% and a maximum increase of 11.95%. The core compression failure presents a small degree of multi-fracture complex failure. With an increase in CO2 exposure time, temperature, and pressure, the triaxial compressive strength gradually decreases, the elastic modulus gradually increases, and the compression failure of shale core is gradually complicated. The variation in mechanical parameters with time, temperature, and pressure under the influence of CO2 real-time contact was quantitatively described. The effect of gaseous CO2 on shale mechanical parameters and core compression failure is significantly weaker than that of supercritical CO2. This research provides theoretical and data support for supercritical CO2-enhanced shale oil and gas recovery and carbon geological storage from a rock mechanics perspective.