Productivity characteristics and distribution modes of multi-layer drainage coalbed methane wells in Hancheng Mining Area

In order to evaluate and understand coalbed methane( CBM) well development effect with multi-layer drainage comprehensively,based on multi-layer draina ge coalbed methane( CBM) well productivity characteristics in Hancheng Mining Area,the productivity distribution modes under different coal seam combinations were also established with dimensionless production stage classification method.The results indicated that most of the CBM wells were observed with high water rate and low gas rat e which needs to be improved urgently.At the end of the water drainage stage,the dimensionless gas rate was about 0.3 while it was about 0.6 when the unstable gas pro duction stage was over. Meanwhile,when end of stable gas production stage occurs,the value of dimensionless gas rate was about 0.8. The gas rate peak appeared in sta ble gas production stage and water rate peak could be found in unstable gas production stage. The effect of the multilayer drainage was better than that of the single layer and the two-layer drainage was better than that of the three-layer. When No. 3 coal was contained in production layers( No. 3+5,3+11,3+5+ 11),the productivity of CBM well was higher than those of No.5+ 11 and sand layers. In the process of the subsequent CBM development,it was considerable to increase the proportion of the wells which p roduced gas from the No.3 coal to improve well productivity. In addition,when well was placed and fractured,it was also important to avoid faults,especially paid more atten tion to monitor whether the coal seams were communicated with aquifers by cracks.