Experimental Study of the Impact of Chlorine Dioxide on the Permeability of High-Rank Contaminated Coal Reservoirs

The permeability of high-rank coal reservoirs is generally low, and high-viscosity working fluid can also contaminate the reservoirs and reduce permeability during drilling and fracturing engineering. These two reasons lead to a lot of low-yield CBM wells in the southern Qinshui Basin, China. The impact of chlorine dioxide on the permeability of high-rank coal has been studied in detail. The coal samples with changed characteristics before and after treatment were compared using coal–ash, displacement, immersion, and plug removal experiments. The ash experiment results show that the ash content of the coal samples decreased by 16.35%. The displacement and immersion experiments using chlorine dioxide solution showed that displacement with chlorine dioxide could increase permeability. The permeability of coal samples increased by 3005.77% after 80 h of immersion. The plug removal experiment results show that the permeability of contaminated coal samples was recovered by 11.10–38.90%, with an average recovery of 27.90%. The experimental results show that chlorine dioxide is effective in improving the permeability of high-rank contaminated coal reservoirs. This research result can be applied to low-yield CBM wells polluted by high-viscous working fluid to increase gas production.