Application of Hydraulic Fracturing and Thermal Effects to Stimulate Gas Liberation from Coal Beds
L. A. Nazarov1, Li Yang2
1Chinakal Institute of Mining, Siberian Branch, Russian Academy of Sciences, Novosibirsk, Russia
2School of Mechanics and Engineering, Liaoning Technical University, Fuxin, China
Keywords: Coal bed, gas emission, borehole, hydraulic fracture, fluid flow, thermal effect, permeability, viscosity, heat and mass transfer model
Abstract
Within the framework of pre-mining drainage of coal beds, the method of thermal treatment of coal using hydraulic fractures is substantiated for the gas liberation velocity and volume enhancement. A geomechanical model is developed and implemented numerically to describe the process of heat and mass transfer in a coal bed with regard to empirical dependences of permeability, thermal diffusivity and sorption properties of coal, as well as viscosity of gas on the temperature and pressure. The authors have solved the problem on methane emission from a horizontal coal bed fractured by two orthogonal and vertically oriented created fractures where fluid heated to 70 °C is was pre-injected, which led to an irreversible increase in permeability. Numerical experiments find out that for the typical thermophysical characteristics of a coal bed under such thermal effect, the volume of gas emission can: rise by more than three times; nonlinearly increase with the length of fractures; slightly depend on thermal diffusivity and limit methane content of coal. the obtained results can be used to enhance efficiency of preparation and mining of coal beds with high gas content.
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