Recent developments in coal mine methane extraction and utilization in China: A review

Over past decades, China has changed the manner in which coal mine methane (CMM) was treated: from mitigating its dangers as a mining hazard to developing its potential as an unconventional gas resource. CMM is rich in China coal seams. These coal seams normally have three distinct characteristics: high pressure, strong adsorption and low permeability. These characteristics require novel extraction and utilization technologies. This paper presented a comprehensive review of how these technologies evolve with time from underground extraction to surface drainage to combined surface-underground approach. Major conclusions include: (1) CMM is mainly drained through underground extraction technologies. In order to improve the drainage efficiency, these technologies usually combine with mining-induced stress relief or other active stimulation techniques and modern borehole sealing techniques; (2) Several innovative surface CMM extraction technologies have been proved as effective for Chinese CMM formation conditions, such as gob surface well extraction, stress-relieved seams surface well extraction, multi-branch horizontal directional surface well extraction, and multipurpose surface well extraction; (3) A combined surface-underground approach has been applied to Huainan and Jincheng coal mines. These applications represent the new development trend of CMM extraction and control in China; and (4) Apart from the CMM extraction technologies, utilization technologies also achieved significant progresses in China. The electricity generation and safe transportation technologies of low-concentration gas have also been developed to improve the gas utilization rate and guarantee the safe long distance and large flow transportation of low-concentration gas in China. The implementation of CMM extraction and utilization technologies has led to a large increase of coal production, gas extraction and utilization, and a significant reduction of fatality.