Analysis and applied study on key factors of coal and rock crack network reconstruction

Liu Xiao; Zhang Fan; Ma Geng; Su Xianbo

doi:10.13199/j.cnki.cst.2017.06.013

Abstract：In order to improve the gas drainage efficiency of low permeable seam,based on an analysis on a "crack network fracturing" of shale gas,fracturing technical idea of a crack network in the coal and rock reservoir of an underground coal mine was provided.With an analysis on the key factors affected to the crack network formation,the Mshale was applied to simulate the three relationship of the hydraulic fracturing fragility index-Poisson' s ratio-single section hydraulic crack volume,the mechanics conditions of the tensile breakdown caused by the natural cracks were judged and the study was conducted on the experiment simulation of the hydraulic fracturing features with different geostress difference.All above showed that under the certain condition of the injection volume,with the fragility index increased,the single section hydraulic fracturing volume would be decreased and the number of the hydraulic fractures would be increased.With the main stress difference increased,the surface area of the sample breaking surface would be increased and would be steadily rough and the fracture opening would be decreased.The smaller intersectional angle between the hydraulic fracture and the natural fractures was,the more easy of the hydraulic fractures would be sheared and damaged along the natural fractures.When the main stress difference was small,the hydraulic fractures would easily have the turn off,bifurcation and other conclusion.Finally,a fracturing experiment of the crack network was conducted in Hebi Zhongtai Mining Company Limited.The effective scope of the fracturing was 21 666 m2,the daily gas drainage volume of a borehole was 13 times higher than before the fracturing of the crack network and was 2.6 times higher thane the conventional hydraulic fracturing.CYT was applied to detect the apparent resistivity variation of the horizontal cross section and the vertical cross section and to confirm the existence of the hydraulic fractured crack network.