Experimental Study on the Influence of Hydrochemical Properties on the Migration of Coal Fines Containing Kaolinite in Propped Fractures

Coal fines generation poses significant challenges tothe efficientextraction of coalbed methane. This study aims to investigate theinfluence of various hydrochemical properties on the migration ofcoal fines containing kaolinite within propped fractures. Experimentaltests are conducted using a coal sample from the No.3 coal seam inthe Shanxi Formation of the Hancheng mining area. The fracture permeability,variation of mass concentration, particle size distribution, and morphologyof the produced fines are analyzed. The results show that under thesame hydrochemical conditions of both Na2SO4 and MgCl2 solutions, the increase of salinity leads tothe increased mass concentration of the produced fines, the increasedpermeability of the core sample, and the decreased particle size ofthe produced fines. Under the same salinity (10,000 mg/L) conditions,the mass concentration of coal fines produced using the Na2SO4 solution is higher than that of the MgCl2 solution, the permeability of the sample is larger, and the particlesize of the produced fines is smaller. Kaolinite added to coal finesincreases the hydrophilicity and promotes coal fines migration. Thepresence of metal cations enhances the aggregation of particles. Theaverage sizes of the produced fines exhibit an increase ranging from14.81 to 49.41%. Similarly, the D90 values exhibit an increase withinthe range of 0.42-34.90%. The aggregation effect of Mg2+ on coal fines is greater than that of Na+. Coalfines migration dredges the propped fractures, leading to an increasein permeability. Coal fines aggregate and block fractures, resultingin pressure rise, which yields a decrease in permeability. In caseswhere the fines aggregation effect dominates, the aggregated finestend to remain in their initial position within the sample throughoutthe experiment. Conversely, if the fines migration effect prevails,the coal fines tend to migrate toward the end of the sample, causingend blockage. This research sheds light on potential strategies foreffectively managing and controlling coal fines.