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.