Technology and practice of coalbed methane drilling and extraction in coal mine areas

There are a large number of high-gas and outburst-prone coal mines across China. Implementing coalbed methane (CBM) drilling and extraction can effectively reduce gas content in coal seams, decrease methane emissions from coal mines, supplement low-carbon energy sources, and enhance the overall efficiency of mining operations. Combining the coal reservoir characteristics and coal production processes, CBM drilling and extraction in coal mining areas can be divided into three stages: pre-drainage in planned and preparation zones before coal mining, extraction in mining-affected zones during coal mining, and post-mining drainage in goaf areas. Corresponding drilling, completion, and extraction techniques are adopted according to different mining stages. For example, factory-style drilling platforms are used for multiple coal seams, inclined drilling rigs drilling technology for shallow-depth seams, densified drilling technologies for thin coal seams, and mining-affected and goaf-specific extraction methods for respective zones to improve coalbed methane well productivity and extraction efficiency. On-site core sampling was conducted to measure residual gas content in coal reservoirs in Jincheng mining area. Data comparison revealed a significant decline in coal seam gas content after years of CBM extraction. Ground coalbed methane drilling and extraction technology in coal mining areas can effectively reduce the gas content in coal mine and ensure safe production, but widespread adoption in coal mines across China remains challenging. It is recommended to strengthen research on coalbed methane extraction technologies in coal mines and further explore extraction methods under different geological conditions.