Study on Mechanical and Microporous Properties Degradation of Coal with Long-Term Adsorption and Its Effect on Coal and Gas Outburst and CO2 Sequestration

Coal is a natural porous medium with a strong adsorption property and is an important energy resource over the world. The strong adsorption property of coal is a causative factor affecting the occurrence of coal and gas outburst. Gas is recognized as the main contributor to the energy release during outburst, and it initiates and maintains the chain process of outburst. Outburst is initiated by the fragmentation and failure of coal, where the adsorption property of coal plays a positive role. Additionally, the pore structure of coal is one of the significant factors affecting the CO₂ sequestration performance. As a widely accepted potential management method for greenhouse gas, CO₂ sequestration in coal seam is affected by the coal-mass properties, seam permeability, and long-term behavior of the sequestrated CO₂. CO₂ adsorption can significantly alter the porous property of coal and affect the CO₂ sequestration capability of coal seams. Both outburst and CO₂ sequestration are subjected to and significantly affected by a long-term sorption process. The former is promoted by the fragmentation of the coal mass induced by adsorption, whereas the latter is threatened by the adsorption-induced fracture. To explore the influence of long-term sorption on the mechanical and porous characteristics of coal, long-term sorption tests were performed. The results indicated that the long-term sorption significantly degraded the mechanical and microporous properties of coal. And, long-term CO₂ adsorption even destroys and pulverizes the coal samples. The findings enhance our understanding of the mechanism underlying the fragmentation of the coal mass during outburst, while may present challenges for CO2 sequestration in coal seam.