Basic problems of hydraulic fracturing for mining and control zone gas in coal seams

The mineral composition,structural system and gas adsorption and desorption effects result in the complexity of hydraulic fracturing in gassy coal seam. The technology of coal seam hydraulic fracturing for regional gas control is still at its initial stage at present. Basic framework of theory,technology and equipment of coal seam hydraulic (fluid) fracturing for regional gas control was proposed. Based on the analysis of physical and chemical property of coal seam, mechanic mechanism of coal seam hydraulic fracturing and the basic spatial morphology of hydraulic fracture were pre- liminarily given. The effects of physical and chemical process,structural transformation,permeability increasing,stress disturbance,displacement methane and water lock of hydraulic fracturing were analyzed. Took the pore pressure gradi- ent as entry point,intensive study should be conducted on the theoretical problems of coal seam hydraulic fracturing. The theoretical problems include the mesoscopic fracture mechanism,the stress disturbance effect and evaluation methodology,the mechanism of volume fracturing mechanism,the displacement methane effect,the migration law and em- bedding property of the proppant,and the drainage and mining law. As for the displacement methane effect,its advan- tages should be used and its disadvantages should be by passed to upgrade hydraulic fracturing for gassy coal seam to hydraulic fracturing displacement methane level. Technical problems such as technology security evaluation criteria, technology,reasonable pumping flow,monitoring of the hydraulic fracture propagation and its effect,application condi- tion and standard require deep-going researches. A set equipment of hole sealing system,analysis software and meas- urement and control system were developed for underground coal seam hydraulic fracturing for regional gas control.