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ABSTRACT
Outbursts comprise the predominant natural hazards in Chinese underground coal mines. Extracting high content gas within coal seams is one of the most effective ways to reduce the risk of triggering outbursts. However, with the depth increase of coal mining production, conventional gas drainage might be failed due to the low permeability of coal seams. Additional permeability enhancement methods should be adopted to improve the gas drainage efficiency. In this study, we proposed the application of liquid carbon dioxide fracturing for enhancing gas drainage in a underground coal mine in China with low permeability coal seams. By drilling cross-seam boreholes, liquid carbon dioxide fracturing was simultaneously performed in the two drilled fracturing boreholes. The effective damage radius of liquid carbon dioxide fracturing was further identified by continuously monitoring pure gas flow rates in different observation boreholes. After liquid carbon dioxide fracturing, there was no significant decrease in pure gas flow rate of observation boreholes for a period of 2 weeks. A conceptual model of liquid carbon dioxide fracturing was proposed for illustrating the mechanisms of improving gas drainage efficiency. Some methods for further optimizing gas drainage with the operation of liquid carbon dioxide fracturing under various thickness of coal seams and geological conditions were discussed. These results suggest that the application of liquid carbon dioxide fracturing are effective for gas control and hazards prevention in underground coal mines.
Acknowledgments
The authors are grateful for the Nantong coal mine, Chongqing Energy Investment Group Co. Ltd, China for providing field test sites.
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Notes on contributors
Yubing Liu
Yubing Liu is a Ph.D student in School of Resources and Safety Engineering, Chongqing University, China. His research field is in experimental rock mechanics and geomechanics.
Zuxun Zhang
Zuxun Zhang is a Ph.D student in School of Resources and Safety Engineering, Chongqing University, China. His research field is in hydraulic fracturing.
Bozhi Deng
Bozhi Deng is a Ph.D graduate in School of Resources and Safety Engineering, Chongqing University, China. His research field is in hydraulic fracturing.
Minghui Li
Minghui Li is a Postdoctoral fellow in School of Resources and Safety Engineering, Chongqing University, China. His research field is in true-triaxial tests, fluid flow in fractured rocks.