干热岩径向井压裂裂缝起裂与扩展数值模拟OA

Hydraulic fracturing is the core technology for the efficient development of enhanced geothermal systems(EGS),but it faces with several significant challenges,including single fracture,difficulty in controlling fracture propagation,and poor connectivity between injection and production wells.To address these issues,a new approach was proposed to steer the directional propagation of hydraulic fractures using radial wellbores in this study.A three-dimensional thermo-hydro-mechani-cal coupled fracture propagation numerical model based on a discrete lattice method was established to elucidate the initiation and propagation characteristics of fractures in hot dry rock(HDR)for radial borehole fracturing and vertical well fracturing.The effects of rock temperature,in-situ stress,injection rate,and fluid viscosity on the directional propagation of fractures guided by radial boreholes were investigated.The results show that the fracture morphology in radial borehole fracturing is dominantly controlled by the re-formed stress distribution around the radial borehole,with fractures initiating and propagating directionally along the radial borehole.In contrast,fractures in vertical well fracturing are mainly influenced by the original in-situ stress distribution and tend to propagate along the maximum principal stress direction.A greater temperature differ-ence between fracturing fluid and rock can enhance thermal stress,facilitating the formation of a complex fracture network,while the steering effect of the radial borehole on fracture propagation may diminish under these conditions.When the in-situ stress difference coefficient ranges from 0 to 0.4,the reformed stress distribution around the radial borehole is large,it can facilitate the formation of multiple directional main fractures.Increasing the injection rate and viscosity of the fracturing fluid can strengthen the steering effect of radial borehole on fracture and significantly increase fracture complexity.