To reveal how mineral
changes affect a coal pore structure in the
presence of water, an autoclave was used to carry out the supercritical
CO2(ScCO2)-H2O-coal interaction
process. To reveal the changes in pore complexity, mercury intrusion
capillary pressure (MICP), low-pressure nitrogen adsorption, CO2adsorption, and field emission scanning electron microscopy
(FESEM) experiments were combined with fractal theory. The experimental
data of MICP show that the MICP data are meaningful only for the pore
fractal dimension with pore sizes >150 nm. Therefore, the pores
were
classified into the classes >150, 2–150, and <2 nm. The
results show that the pore volume and specific surface area of the
coal increased significantly after the reaction. ScCO2-H2O can cause the formation of many new pores and fractures
in the coal. The presence of H2O may increase the potential
for the injection of CO2into the coal seam. The complete
dissolution of calcite surfaces caused a significant increase in the
pore volume and specific surface area of the pores >150 nm. The
morphologies
of these pores are controlled by the morphologies of the complete
dissolution carbonate particles. The pore morphologies were relatively
uniform, and the fractal dimensions decreased. However, the incomplete
dissolution of calcite leads to irregular variations in the morphologies
for the pores in the 2–150 nm pore size range. The pore morphologies
that are produced by incompletely dissolved calcite particles are
more complex, which increases the fractal dimensions after the reaction.
The fractal dimensions of the pores <2 nm decreased after the reaction,
indicating that the newly generated micropores were more uniform and
had regular pore morphologies.