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Abstract:
In this study, we used the Particle Flow Code 2D (PFC2D) to simulate interaction of hydraulic fractures and natural fractures
in low permeable hard rock. Natural fractures are simulated using the smooth joint model of PFC2D. We modified our fluid flow
algorithm to model larger fracture permeability, and we investigated interactions of hydraulic fractures and natural fractures
by varying the angle of approach and viscosity of the fracturing fluid. We also investigated seismic events evolving in a complex
fracture network. The results demonstrate that our modelling tool is able to capture all possible interactions of hydraulic
and natural fractures: Arrest, Crossing, Slippage of hydraulic fracture, Dilation of natural fracture, Closing/Opening of natural
fracture. With low angle of approach, the hydraulic fracture coalesces with the natural fractures and results in hydro-shearing
and propagation of hydro-wing fractures at the tips that are mostly Mode I type. We tested the model containing multiple natural
fractures with varied fluid viscosity. Hydraulic fracture generated by high viscosity fluid tends to be localized, linear and less
influenced by the natural fractures. In the complex network of natural fractures, fluid columns built along the fracture network
increase the local state of stress by stress shadowing. Hydro-shearing of the natural fractures that were under increased stress
state can be explained as the main mechanism responsible for occurrence of larger magnitude microseismic events.
