Background  In the coal mining areas of China, coalbed methane (coal mine gas) occurs under complex conditions, rendering it difficult to achieve its efficient resource exploitation and effective hazard control using a single technique.

Advances As indicated by the current state of the research, development, and engineering application of coalbed methane (coal mine gas) drainage techniques in China in recent years, the drainage methods can be classified into three categories according to their spatial arrangements: surface drainage, underground drainage, and surface-underground combined drainage. Furthermore, the surface and underground drainage methods can be subdivided into four types based on their temporal arrangements: surface pre-drainage, underground pre-drainage, surface drainage through mining-induced pressure relief, and underground drainage through mining-induced pressure relief. Among these, the pre-drainage methods are primarily applicable to coalbed methane (coal mine gas) pre-drainage before coal seam mining, whereas the drainage methods through mining-induced pressure relief are primarily used for gas control during coal seam mining. This study presents a comparative analysis of primary techniques and their characteristics for various drainage methods. The analysis results reveal that primary techniques for surface pre-drainage include vertical wells (cluster wells), remotely connected horizontal wells, multi-branch horizontal wells, and multistage fracturing using horizontal wells; techniques for surface drainage through mining-induced pressure relief are dominated by vertical and L-shaped wells; principal underground pre-drainage techniques comprise in-seam drilling, crossing-seam drilling, and pneumatic directional drilling; and techniques for underground drainage through mining-induced pressure relief are composed primarily of crossing-seam drilling and high-level directional drilling. Additionally, the surface-underground combined drainage techniques refer primarily to those that enable efficient gas drainage by connecting the underground directional long boreholes to the fracturing range of surface wells. These techniques are primarily used to rapidly achieve effective gas drainage in the preparation areas of coal mines. Based on their applicable geological and coal-engineering conditions, the application effects of various drainage techniques in their demonstration projects in representative coal mines are analyzed. The results indicate that multistage fracturing using horizontal wells and L-shaped wells represent efficient techniques for surface pre-drainage and surface drainage through mining-induced pressure relief, respectively. In contrast, the engineering quality and effectiveness of underground pre-drainage and underground drainage through mining-induced pressure relief are primarily controlled by the directional drilling process and its technical level.

Prospects  Based on the trends in the coal and coalbed methane (coal mine gas) industries of China, this study proposes four key development directions of techniques for coalbed methane (coal mine gas) drainage in coal mining areas: surface-underground combined gas drainage, the coordinated exploration and exploitation of deep coalbed methane and coal resources, the synergistic control of multiple hazards, and the recovery and utilization of coalbed methane resources in closed mines.