A comparative study of hydraulic fracturing with various boreholes in coal seam

Comparative numerical study on hydraulic fracturing with various boreholes in coal seam combined with in situ experiments was carried out to investigate the fracturing mechanism and loosening effect of hydraulic fracturing in coal seam. Hydraulic fracturing models with single-borehole, three-borehole and fiveborehole were built based on in situ tests in Chengshan coalmine, Jixi city, Heilongjiang province, China and the changes of water pressure and shear stress around boreholes during hydraulic fracturing were analyzed. The influence of hydraulic fracturing with controlling borehole on crack initiation and propagation was discussed. According to the in situ testing results, it is found that controlling boreholes in hydraulic fracturing not only can control the direction of crack propagation, but also can judge the effect of crack initiation and breakdown. The work in this paper is of great importance for the design of hydraulic fracturing technology and the alternative of the parameters in theory and practice.