ABSTRACT
Coal and rock mass is a kind of porous media consist of many cracks and pores, these cracks and pores in the original state is mostly mutually connected. When making water injection borehole, crack will produce in coal and rock around borehole. These fissure circles are interlaced with coal native fissures. Hydraulic Fracturing use the initially fissures of water injection borehole, putting high-pressure water into the coal rock, to overcome coal rock fracture surface minimum principal stress and the tensile strength of coal and rock, making these fractures occurred after effects of high pressure water expansion and extension, thereby forming an internal split seam, forming a number of interwoven multi-fractured connected network. The formation of the network had created conditions for the flow of the gas in the coal seam,
1 INTRODUCTION
In recent years, most mines of our country have entered a phase of deep mining, the stress increasing that comes along makes the seam and rock permeability get worse, gas pressure and gas content has greatly increased[1]. According to statistics, more than 95% of the high gas and outburst mines coal seam in our country have a low coal seam permeability, gas extraction is difficult, drainage is not ideal[2]. To improve the coal seam permeability, domestic and foreign scholars have proposed a variety of methods, such as hydraulic cutting, hydraulic punching, hydraulic fracturing, loosening blasting, protective layer of pressure relief. Due to the simple process and broad applicability, the hydraulic fracturing has been more and more applied[3-6].
