Analysis of the influence of water injection flow rate on the dynamic expansion law of cracks across interfaces

MA Dengyun; MA Yankun; WANG Xiaoqi; ZHOU Jian

doi:10.19956/j.cnki.ncist.2025.02.013

Abstract：In order to investigate the influence of water injection flow rate on the dynamic expansion process of fractures across interfaces,a single-sided visualization true triaxial hydraulic fracturing test system is used to conduct roof guided hydraulic fracturing tests,and the changes in water pressure curves and the distribution characteristics of fracture networks during the expansion process of fractures across interfaces are studied.The research results show that:When the water injection flow rate increases from 60 mL/min to 100 mL/min,the initiation pressure increases from 4.57 MPa to 8.50 MPa,and the initiation time shortens from 12 seconds to 6 seconds;With the increase of water injection flow rate,the total length of fractures and the length of rock frac-tures show a decreasing trend;The length of coal seam cracks shows a trend of increasing first and then decrea-sing,and when the water injection flow rate is 80 mL/min,the proportion of coal seam crack length reaches a maximum of 39.78%;Using fractal theory to quantitatively compare and analyze the fracture network under dif-ferent injection flow rates,it is found that with the increase of injection flow rate,the fractal dimension de-creased from 1.3775 to 1.2160,indicating that the complexity of the fracture network is decreasing.The fractal dimension of the rock layer shows a decreasing trend with the increase of injection flow rate,and the fractal dimension of the coal seam shows a trend of first increasing and then decreasing with the increase of in-jection flow rate,reaching a maximum value of 1.1834 at an injection flow rate of 80mL/min.The research re-sults can provide reference for the process parameter design of hydraulic fracturing technology for roof.