Experimental Study on Mechanical Properties Degradation and Acoustic Emission Characteristics of Coal Rock Caused by CO₂ Injection

Geological sequestration of greenhouse gases has gained extensive attentions in recent years, but the degradation law of mechanical parameters and the acoustic emission (AE) characteristics of coal under triaxial loading with CO₂ injection are still unclear. In this work, a self-balancing triaxial apparatus was independently developed to successfully obtain the degradation law of coal mechanical properties and AE characteristics caused by CO₂ injection under triaxial loading. The test results show that: (1) the triaxial compressive strength and elastic modulus of coal samples decrease with the increase of CO₂ injection pressure. The maximum decrease of triaxial compressive strength of coal sample is 21.25% (injection pressure is 1.2 MPa, confining pressure is 1.5 MPa), and that of elastic modulus is 4.44% (injection pressure is 1.2 MPa, confining pressure is 1.5 MPa). (2) The AE activities of coal samples during triaxial compression can be divided into four stages: quiet period, steady increase period, surge period and stable period. The AE activities are well coupled with the stress–strain curve and the failure of coal. These results provide a basis for CO₂ geological storage, theoretical research and disaster prevention and control.