In the developing of the hydrothermal or shale oil and gas reservoir, hydraulic fracturing method is widely used today. It creates fracture nets around the well and improves the permeability, which enhances the production of those resources. However, it is challenging task to predict the direction and area of the hydraulic fracturing due to the complicated in-situ stress field. Fracturing to the unexpected area might cause induced seismicity or environmental pollution. It is, therefore, quite important to estimate how fractures are creates in the reservoir to get the idea of the production of resources and prevent the environmental pollution. We focused on how the pre-existing fractures propagate with the steady and non-steady injection pressures. In this study, especially we could adopt the multiple pre-existing fractures, which exist symmetrically around the borehole. To deal with the multiple fractures in the hydraulic fracturing simulation is much important to understand the realistic behavior of the fracture propagation. We simulated how the fractures could propagate with the steady and non-steady hydraulic pressure during the water injection. We could obtain two results from our numerical simulations: First, the curvature of the fracture trace depends on hydraulic pressure with the both cases of the steady and non-steady pressure, but no matter how the fluid pressure is, the orientation of fracture propagation finally converges to that of maximum principal stress. Second, the transition of the stress field follows the change of the injection pressure after some seconds, which means the delayed response of the fracture propagation in the non-steady hydraulic pressure condition. The simulation scheme of this study can deal with multiple fractures so that it could realize the quantitative estimation of fracture propagation in the complex stress region including various scales of fractures in the future.


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