Fracture initiation characteristics of horizontal drilling fracturing in underground coal mine

ZHAO Kaikai; ZHU Kaixiong; FENG Yanjun; SUN Xiaodong; ZHENG Yangfa; WANG Peng; WANG Yu

doi:10.11799/ce202503018

Abstract：To clarify the characteristics of fracture initiation in horizontal drilling in coal mine,a theoretical calculation model was established based on the regression equation of in-situ stress,the stress distribution of borehole wall and the maximum tensile stress criterion,and the influence of the depth and orientation of borehole on fracture initiation parameters were studied.The 3D discrete lattice numerical method was used to simulate the evolution of fracture initiation in horizontal drilling fracturing.The results show that the fracture initiation pressure is influenced by the buried depth of formation and the azimuth of borehole.The fracture pressure is positively correlated with the buried depth.When buried depth increases from 150 m to 1100 m,and the peak fracture pressure increases by 46.47 MPa.When the buried depth is less than 1100 m,the fracture initiation pressure increases first and then decreases with the increase of the drilling azimuth.The borehole azimuth corresponding to the abrupt point of fracture initiation parameter decreases monotonically with the increase of burial depth.The crack initiation pressure reaches its peak near the mutation point,and the crack initiation positions all changes from 90° to 0°.The fracture direction angle suddenly increases from about 0° to a certain positive value,and then presents a parabolic change characteristic,and the fracture direction angle is less than 27.08° within 1100 m buried depth.The fracture initiation of borehole fracturing is a multi-stage evolution process,including the stages of micro-fracture initiation,hole wall fracture line development and macroscopic fracture elliptic self-similar expansion.The research conclusion can provide reference for the optimization design of borehole layout scheme in underground coal mine.