Experimental study of coal fines migration characteristics in reservoirs with diverse coal structures: Influence on reservoir behavior

Abstract

The challenge of coal fines production within tectonic coal reservoirs during coalbed methane (CBM) development in China presents a significant concern. In this study, coal samples with distinct coal structures from Hancheng mining area were selected for experiments on coal fines migration. Our analysis focused on the distinctive characteristics of coal fines generated by various coal structures, the subsequent alterations in sample permeability, and the changes in pore and fracture structures before and after the experiments. By examining the reservoir properties across different structures, we aimed to uncover the migration characteristics of coal fines in these diverse coal reservoirs and understand their influence on reservoir behavior. The results revealed distinct characteristics of coal fines among reservoirs with different structures. Under the same conditions, the average mass concentration of coal fines produced by cataclastic coal (CC) and granulated coal (GC) was observed to be 1.15–35.33 and 2.27–51.74 times higher than that of primary structure coal (PC), respectively. Coal fines generated by reservoirs with varying structures exerted different effects on pore-fracture structure and permeability. The average permeability ranges of the PC, CC and GC samples during the experiment were 0.27–0.66 mD, 0.33–1.58 mD and 8.96–19.38 mD, respectively. The PC and CC being less affected by tectonic deformation and possessing higher strength, exhibited minimal impact on their permeability. Conversely, the GC displayed the highest degree of structural deformation, lower strength, and unstable pore structure, significantly affecting its permeability. These findings offer valuable insights into coal fines production and reservoir behavior in CBM development, particularly in reservoirs featuring diverse coal structures.