Supercritical CO2 induced development of macropores/fractures in coal and associated mineral precipitation

• Fractures in coal were found to propagate along mineral layer under supercritical CO 2 exposure. • It was discovered that secondary minerals generated by macropores/fractures evolution adhered to the pore walls, forming a microscale mineral overlay. • Microscale mineral precipitation was confirmed to result from macropores/fractures expansion driven by nanopores’ dissolution. CO 2 sequestration in deep reservoirs provides dual benefits of energy exploitation and reduction of greenhouse gases. In deep coal seams, supercritical CO 2 (SCCO 2 ) initiates complex physical and geochemical interactions, driving pores/fractures’ evolution, altering reservoir’s permeability and constraining storage security. Micro-CT imaging showed that the volumes of macropores/fractures and minerals in anthracite increased by 95.24% and 83.33%, respectively, after saturation with SCCO 2 . The propagation paths of the fractures were dictated by the mineral layers, extending preferentially along weak bedding planes. Concurrently, the dissolution of minerals induced by SCCO 2 generated secondary precipitates on the surfaces of macropores/fractures, consequently enhancing their roughness. These findings confirme a multiscale evolution mechanism in which nanopore dissolution drives the expansion of macropores/fractures, providing theoretical support for CO 2 sequestration in deep coal reservoirs and the synergistic development of coalbed methane.