Character and inspiration of coalbed methane extraction from underground boreholes

Coalbed methane (CBM) has become an important unconventional gas source in China, yet quantitative understanding of underground borehole extraction remains limited. Based on field data from the Wangpo coal mine, this study investigates the relationships among methane concentration, vacuum pressure, gas production rate, and cumulative extraction behavior. Results reveal that daily production rates follow a power-law–type decline consistent with pore–cleat–controlled gas flow, and the cumulative extraction curve can be divided into four characteristic stages corresponding to shifts in gas-migration mechanisms. The rate integral–derivative function exhibits a strong linear correlation with mass-balance time, underscoring its potential as a predictive tool for production forecasting. A clear threshold effect of vacuum pressure is identified, beyond which methane concentration improves significantly, while longer boreholes enhance gas capture due to increased exposed coal area. However, drilling length, cost, and geological heterogeneity must be balanced to maintain efficiency. The findings highlight the need for intelligent vacuum-pressure regulation based on real-time methane monitoring to optimize extraction stability and utilization efficiency. These insights offer practical guidance for CBM borehole management and process optimization.