Hydraulic Fracturing Theory of Coal-Rock Mass and Its Technical Framework

The structure transform of coal-rock mass is an universal scientific issue for solving many technical problems in coal mine.Hydraulic fracturing is an effective method to transform the coal-rock structure.Aiming at this issue,we analyzed the structure and physico-mechanical properties of coal-rock mass and the hydraulic crack propagation and physical chemistry effect of hydraulic fracturing of coal-rock mass.On this basis,we propose the corresponding hydraulic fracturing control technology and analyze its application in coal mine.The internal structure of coal is composed by four-stage spatial structure system which comprises crack-cleat and stratification-micro fissure-pore.The soft texture of coal,the effect of gas adsorption analysis,the development of natural fractures,and other factors make the hydraulic fracturing of rock-mass complicated.In order to meet the structural transformation,strength decrease,permeability increase,and other engineering needs,the process of hydraulic fracturing for coal rock mass is from the propagation of main hydraulic cracks,the propagation of airfoil branch fissures propagation,and water absorption wetting.The focuses of these three effects are different on different projects.Directional fracturing technology with beforehand hydraulic slotting has been proposed.The weakening strength and increasing permeability technology of hydraulic blasting fracturing has been put forward.The experimental results have proved that the hydraulic fracturing,after water pressure control blasting,is an efficient way to increase the number and range of hydraulic cracks.Hydraulic fracturing of coal-rock mass can be used to control hard roof,to weaken the hard top coal,to transfer the stress directionally,to release the local concentrated stress,to weaken the strength and shock,to increase the permeability of gas-filled coal seam,and to prevent coal-gas from outbursting,and so on,.