Abstract
Most coal reservoirs in China have low permeability, which causes gas drainage to be inefficient. The method of cyclic cryogenic fracturing basing on freezing–thawing (F–T) fracturing effects is proposed to break coal to increase its permeability. An F–T experiment was carried out at different freezing temperatures using a nuclear magnetic resonance (NMR) test and an ultrasonic test. We investigated the evolution of coal pore structure under different freezing temperature F–T cycles and the mechanism of F–T fracturing. The results indicate that the frost force and the thermal stress in the cyclical process of F–T work together to cause fracture formation and fatigue damage. When the freezing temperature decreases, the network of pores and fissures becomes more developed and the number of mesopores, macropores and micro-fractures increases. This suggests that the network of pore-fractures in coal will be more interconnected and the space available for gas seepage will be larger. Ultimately, this significantly increases the efficiency of gas drainage.
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Acknowledgements
This work was financially supported by the National Natural Science Foundation of China (51774278, 51274195, U1361106), the Natural Science Foundation of Jiangsu Province (BK20170001), the National Major Scientific Instrument and Equipment Development Project (2013YQ17046309).
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Sun, Y., Zhai, C., Qin, L. et al. Coal pore characteristics at different freezing temperatures under conditions of freezing–thawing cycles. Environ Earth Sci 77, 525 (2018). https://doi.org/10.1007/s12665-018-7693-y
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DOI: https://doi.org/10.1007/s12665-018-7693-y