Microscopic propagation of hydraulic fractures under different confining pressure and stress differences

ZHANG Pengfei; FENG Gourui; WANG Pengfei; FAN Yijiang; WEN Xiaoze

doi:10.11799/ce202510016

Abstract：The stress environment of coal mining can be effectively improved by hydraulic fracturing technology.Studying the stress-induced microscopic cracking and expansion patterns of hydraulic fracture is essential for advancing the theory of fracturing control and optimizing the selection of fracturing locations.Using MatDEM software,hydraulic fracturing simulation tests were conducted under two different conditions:constant confining stress and stress difference.The results indicate that:Firstly,the hydraulic fractures under constant confining pressure are distributed at 120° due to the uneven distribution of particles around the borehole wall and the priority expansion of unilateral fracture.In the presence of stress difference,the main fracture is straight and single.The compressive stress concentration area distributed at both ends of the fracture is negatively correlated with the stress difference,and a tensile stress fracture mode is visible at the tip.Secondly,the curve of pumping pressure growth rate initially sharply increases and then gradually stabilizes,indicating hydraulic fracture penetration.This pattern is consistent with the fluctuation characteristics of the cumulative increase velocity of micro-cracks.According to the above indexes,the fracturing process can be divided into four stages:no micro-cracks,slow growth of micro-cracks,steady growth of micro-cracks,and rapid growth of micro-cracks.Thirdly,high confining pressure promotes the initiation of fractures and inhibits the development of the fracture process zone.A high stress difference enhances the control of fracture initiation and propagation,which is reflected in the connection and closure of branch cracks.Fourthly,to ensure that the hydraulic fracture meets the requirements of the working conditions,the fracturing area is selected based on the minimum horizontal principal stress and stress difference.This approach allows for better control over both the main fracture and branch fractures,and helps to mitigate any potential adverse effects caused by stress disturbance during fracturing operations,particularly in areas with high stress differences.