Experimental Investigation on the Impact of Coal Fines Migration on Pores and Permeability of Cataclastic Coal

During the production process of coalbed methane, thegenerationand migration of coal fines can obstruct fractures in coal reservoirsand reduce their permeability. In order to investigate the effectsof coal fines migration on the porosity and permeability of coal reservoirs,we conducted core water flooding experiments, low-field nuclear magneticresonance (NMR), and low-temperature N-2 adsorption experimentsto study the variations in porosity and permeability of cataclasticcoal during coal fines migration and the impact of coal fines migrationon porosity and permeability. The experimental results reveal thatthe initial porosity ratio of cataclastic coal exhibits the characteristicsof micropore > macropore > transitional pore > mesopore,with thepore types being predominantly fissured. The porosity of pores largerthan 1000 nm and those larger than 10,000 nm exhibit consistent trendsbefore and after water flooding, indicating that the blockage or unblockingof pores with radius larger than 10,000 nm by coal fines can alsocause blockage or unblocking of some interconnected macropore. Theearly stage of flooding is the main period for coal fines migrationand production in cataclastic coal, during which the mass concentrationof coal fines production is higher and some macropores and fracturesbecome blocked, resulting in a larger decrease in porosity. The higherthe initial permeability of cataclastic coal samples with a largerend-face fracture density, the more similar the variations in porosityand permeability of pores larger than 10,000 nm during the floodingexperiment, indicating that coal fines mainly block interconnectedpores and fractures with radius larger than 10,000 nm through migration,thereby reducing permeability. This study provides a theoretical basisfor the efficient production of coalbed methane.