Numerical simulation of three-dimensional fracture interaction

The exploration and production of unconventional reservoirs, such as tight-gas sand, gas and oil shales, and geothermal deposits, require hydraulic fracturing treatments to increase reservoir permeability and enhance its production. However, the presence of natural fractures alters hydraulic fracture propagation through the rock formation. This interaction may lead to complex fracture networks, which can connect with shallower aquifers or geological faults increasing the risk of fault reactivation. This work presents a numerical technique using the finite element method to study the interaction between hydraulic fracture and natural fractures to predict the direction of fracture propagation. Fractures are modeled using a coupled hydro-mechanical zero-thickness interface element. A damage constitutive relationship describes the behavior of the hydraulic fractures. Natural fractures follow the Mohr-Coulomb constitutive model. Three-dimensional numerical models are simulated to study hydraulic fracture propagation and its interaction with pre-existing natural fractures. The numerical results show good agreement with experimental tests. The three main possibilities of fracture interaction (arrest, opening, and crossing) are predicted. The effect of in-situ stresses, fracture orientation, friction angle, injection flow rate and distance from the borehole to natural fracture are also investigated. The results highlight that the most important parameters affecting fracture interaction are the in-situ stresses and angle of approach between hydraulic fracture and natural fracture. Finally, this methodology can support the prediction of complex fracture network behavior in field conditions.