Abstract: In order to reveal the initiation mode and controlling factors of hydraulic fracture as well as its propagation characteristics near the interface between production layer and barrier, a FEM-based code is employed and several numerical models are built to emphatically discuss the possibility and necessary conditions of the formation of double fractures.The penetration phenomenon of hydraulic fracture near the interface between production layer and barrier is also numerically simulated.Numerical results show that the differential stress and perforation azimuth play an important role in the initiation mode of hydraulic fractures.Either a higher differential stress or a higher azimuth can decrease the possibility of fracture initiation and propagation along the perforation direction.If the cement sheath is failed, a fracture near the well may initiate along the orientation of maximum principal stress.If both mechanical and hydraulic conditions are satisfied, a double fracturing mode, i.e.two fractures initiating synchronously along the orientation of perforation and maximum principal stress, could be obtained.During propagating, a weak interface between production layer and barrier may terminate the fracture or induce the formation of T-shape fracture.A barrier with lower elastic modulus may help a fracture penetrate through the interface and continue to propagate.The numerical results in this study are expected to provide some references for the perforating parameters optimization and fracturing design of horizontal wells.

Key words: perforation, double-fractures, interface, numerical simulation, hydraulic fracturing, horizontal well