Pore Size Evolutionary Mechanism of Anthracite Induced from Water–Rock Interactions

The control effect of water-rock interactions on the pore structure strongly influences the extraction efficiency of coalbed methane. In this study, the #3 coal seam in the Fanzhuang block was taken as the research object, and a physical simulation cross experiment involving water-rock interactions was designed with different mineralization rates and different flow rates. The changes in the coal pore structure were compared to and analyzed under different experimental environments. The results show that the water-rock interaction sites are concentrated in the range of meso- and macropores. It can be shifted to micropores and small pores under the action of high mineralization and flow rates. The micropores and small pores gradually merge and transform into mesopores with the dissolution of soluble minerals in the process of water-rock interactions. Macropores undergo a weakening of cementation, causing the cementitious mineral particles to decompose and refill, thereby transforming into mesopores. Moreover, the dissolution of minerals leads to an increase in the ion concentration, pH value, and mineralization in the solution; moreover, the solution is weakly alkaline. In addition, the aqueous solution with a flow rate of 0.30 mL/min and high mineralization had a relatively strong effect on the pore structure. The results of this study can provide a theoretical reference for the optimization of coal-bed methane production systems.