Simulation and experimental research on upward cross-seams hydraulic fracturing in deep and low-permeability coal seam

Long-time and high-efficiency CBM drainage is a problem for current CBM disasters control and CBM re- source utilization. Numerical simulation and engineering experiments were conducted to systematically study the under- ground hydraulic fracturing technique for greatly increasing the permeability of coal seam. The research results show that there are five stages in the process of hydraulic fracturing,including energy and stress accumulating,micro cracks growing,local damage, local cracks growing and connecting, and fail to resistance of coal and rapid expansion of cracks. A large number of cracks created by hydraulic fracturing,and swelling effect of roof and floor make coal seam pressure relieved,thus,the permeability of coal seam is greatly increased. The engineering experiments validate the mi- gration path of water,and it is in agreement with numerical simulation results. A large-range permeability increase and long-time CBM drainage are achieved. This study provides a technical way for intensified permeability increase and high-efficiency CBM drainage in deep and low-permeability coal seams.