Abstract:
ScCO
2-H
2O-coal geochemical reaction can exert a great influence on the physical and chemical structure of coal, playing a critical role in the CO
2 injection and enhancing CH
4 recovery. To investigate the effects of ScCO
2-H
2O on chemical structure in coal, three coal samples of different metamorphic grades were exposed to supercritical CO
2 and deionized water under 1000m depth temperature and pressure conditions for 240h using a high pressure reactor(ScCO
2/H
2O simulation system and coal/rock geochemical reaction device). X-ray diffraction and Raman spectroscopy were used to provide change characteristics of crystal structure and carbon order degree of coal before and after the ScCO
2-H
2O treatment. The results show that the ScCO
2-H
2O reaction destroys the crystal structural integrity and carbon order degree and changes the macromolecular structure of coal, the effect mainly depends on the coal rank, i.e., for low rank coals, the degree of parallel orientation increases and makes its structure more compact, the lamellae spacing decreases; while for medium-high rank coals, the disordered structure and lamellae spacing of the coal microcrystalline structure increases. This study result has laid a micro-scale foundation for the adsorption/desorption, pore and permeability characterization of coal reservoir before and after ScCO
2-H
2O action in the implementation of the CO
2-ECBM project.