Experimental study on physical simulation experiment of hydraulic fracturing dynamic evolution in coal and rock mass .

In order to master the time-space evolution law of the stress field and the hydraulic pressure field near the fracturing boreholes during the hydraulic fract uring process of the coal mass, the physical simulation test system of the multi-field coupling coal bed methane mining was applied to the experiment study.The test res ults showed that the full process of the hydraulic fracturing could be divided into four stages and they were stress accumulated stage, micro crack development stage, fr acture stability lost and expansion stage and after the cracking stage .During the hydraulic fracturing process, the radial stress of the fractured borehole would be varied obviously and the stress variation parallel to the direction of the fractured borehole would not be obvious.Within the crack expanded scope, the location with a distance more far to the fractured section would be late to have a stress increased. During the hydraulic fracturing process, the hydraulic pressure field evolution would have a cl osed relationship to the crack development and expansion. The hydraulic pressure isoline would be inclined to be developed along the direction of the crack expansion. The expansion speed of the hydraulic pressure isoline along the maximum principal stress direction would be higher than the expansion speed along the direction of the central principal stress and minimum principal stress, which shows that the hydraulic fracturing crack is mainly along the maximum principal stress direction.