Study on the deterioration and damage evolution characteristics of mechanical properties of siltstone after supercritical CO2 treatment

To quantitatively represent the deterioration law of the mechanical properties of siltstone after exposure to supercritical CO 2 (SC-CO 2 ), experiments were conducted to test the mechanical parameters of rocks under the coupling effect of CO 2 –water–rock interactions. The purpose of this study is to determine the evolution law and damage characteristics of each siltstone mechanical parameter under the action of SC-CO 2 . In combination with numerical simulation results, this study revealed the damage evolution characteristics of rocks in a CO 2 geological storage reservoir. The research findings indicate that SC-CO 2 exhibits a certain time effect and causes non-uniform damage to siltstone. Both the deterioration law of the mechanical parameters and soaking time exhibited an exponential relationship. With increasing soaking time, both the uniaxial compressive strength and elastic modulus showed a decreasing tendency, whereas the Poisson's ratio showed a varying degree of increase. The total degree of deterioration gradually increased as the soaking time increased and approached a stable value. After exposure to SC-CO 2 , the damage deformation and failure mode transitioned from brittle to plastic in the siltstone samples. In addition, there was a shift from a single axial crack failure pattern to a complex failure mode with multiple cracks. This study also derived a uniaxial compressive strength prediction model for siltstone based on soaking time, constructed an elastic modulus damage model, and established a fluid–solid coupling model considering damage in the CO 2 geological storage process. The experimental and numerical simulation results revealed that microstructural alterations occurred in the siltstone after exposure to SC-CO 2 . Furthermore, it was discovered that damage accumulation from the micro- to macroscale ultimately led to a gradual deterioration in mechanical properties. The research results provide a theoretical basis for mechanical stability evaluation in CO 2 geological storage. • By analyzing the peak stress evolution law of uniaxial loading failure of sandstone samples soaked in supercritical CO 2 , combined with the characterization results of sample failure modes, the uniaxial loading failure mechanism of sandstone considering the effect of soaking time was revealed. • Based on the degradation law of mechanical properties of sandstone after supercritical CO 2 immersion, a prediction model for uniaxial compressive strength and elastic modulus damage of sandstone based on immersion time were established. • A stress seepage damage coupling model for supercritical CO 2 geological storage was established, and the coupling relationship between reservoir stress and damage variables was analyzed, revealing the evolution characteristics of CO 2 geological storage reservoir damage.