Recharge water types of coalbed methane wells: Controlling effects on water yield and countermeasures

External water recharge of coalbed methane (CBM) wells leads to high water yield, thus affecting effective pressure propagation within coal seams and ultimately impacting gas production. This study aims to ascertain the influence of different types of recharge water on the water yield of CBM wells, as well as the characteristics of water yield and gas production of these wells under different recharge water types. Based on the exploration and development data of 25 CBM wells in the Shouyang block, this study presented general methods for obtaining the parameters for recharge water type classification and proposed the stepped method for the type classification. As a result, this study determined the recharge water types, analyzed their controlling effects on the water yield of CBM wells, as well as the characteristics of water yield and gas production curves, and proposed countermeasures against different types of recharge water. The results are as follows: (1) The recharge water of CBM wells can be divided into three types, namely surface water, surrounding rock water, and no recharge. Among them, the surrounding rock water recharge can be further divided into the fault connection type, the interlayer breakthrough type, and the lateral recharge type. (2) The moderate and high water yields in the Shouyang block are distributed primarily in the northern, southwestern, and southern parts of this block. The coal seams in the northern part are shallowly buried, and the surface water is the main recharge source of CBM wells. In the southwestern part, the surrounding rock water recharge of the fault connection type is the main factor controlling the high water yield of CBM wells. In the middle and southern parts of the Shouyang block, the surrounding rock water recharge of the remaining two types is the main factor controlling the high-yield water of CBM wells. Finally, this study verified the reliability of the classification method by applying this method to the southern Shizhuang block and proposed the development countermeasures against different recharge water types: (1) Areas with surface water recharge are generally characterized by low gas content, and CBM wells in these areas generally exhibit low gas production and high water yield. Therefore, it is necessary to arrange CBM wells prudently in these areas; (2) Areas with lateral recharge show high water yield, and thus CBM wells should be kept away from runoff in these areas; (3) Areas with surrounding rock water recharge of the fault connection type exhibit high water yield and unstable gas production. Therefore, it is recommended that no CBM wells should be arranged in these areas; (4) For areas with surrounding rock water recharge of the interlayer breakthrough type, the optimization of fracturing parameters and the synergistic drainage-based depressurization of the well pattern hold the key to high gas production; (5) For areas with no recharge, it is prone to achieve drainage-based depressurization, and the optimization of fracturing and production processes plays an important role in guaranteeing high CBM production in this area; (6) For areas with multiple recharge water types, it is difficult to develop CBM, and it is necessary to arrange CBM wells prudently in these areas.