3D Fracture Model for Multistage Fracturing in Deep Ductile Rocks Based on Thermal-Hydraulic-Mechanical Coupling Cohesive Zone Model

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Summary: Quantitative prediction of hydraulic fracture (HF) propagation in horizontal wells has become an important research topic in recent decades. The thermal-hydraulic-mechanical (THM) behavior of HFs in deep ductile rock is complicated, especially when the fracturing fluid is compressible and its viscosity is temperature/pressure sensitive. Traditional HF models ignore the ductile behavior of rock breakage and the changes in thermal/physical properties of fracturing fluid. For this study, we developed a coupled THM 3D fracture model (MFrac3D) for multistage hydraulic fracturing in deep ductile rocks. Fracture opening, rock deformation, and heat transfer are coupled with fluid flow inside the HF. Compressibility and temperature/pressure-sensitive viscosity of fracturing fluid are first considered in this model. The cohesive zone model (CZM) is used to determine the ductile failure at the fracture tip of deep rock. MFrac3D is accurately verified by the analytical solutions and physical fracturing experiments. The temperature field inside the HF is dominated by the convective heat carried by the fracturing fluid. The ductile failure of deep rock affects not only the fracture tip geometry but also the injecting pressure and HF width distribution. For simultaneously propagating HFs, the ductile failure of deep rock also affects the stress interference strength among them.

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