Contents lists available at ScienceDirect Computers and Geotechnics journal homepage: www.elsevier.com/locate/compgeo Research Paper Numerical simulation of three-dimensional fracture interaction Eleazar Cristian Mejia Sanchez (Dr) a , Julio Alberto Rueda Cordero (Msc) a,b , Deane Roehl (Professor) a,b, ⁎ a Tecgraf Institute, Pontifical Catholic University of Rio de Janeiro, 22451-000 RJ, Brazil b Department of Civil and Environmental Engineering, Pontifical Catholic University of Rio de Janeiro, Rua Marquês de São Vicente, 225, Gávea, 22453-900, RJ, Brazil ARTICLE INFO Keywords: Fracture interaction Hydraulic fracture Fractured reservoirs Frictional fracture behavior Hydromechanics ABSTRACT 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 in- terface 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 re- sults 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. 1. Introduction Hydraulic fracturing is one of the main stimulation techniques to improve oil and gas recovery from unconventional reservoirs. However, the stimulation of these reservoirs can lead to environmental problems such as fault reactivation induced by the interaction with a hydraulic fracture [1]. Unconventional reservoirs often contain natural fractures, which affect the propagation of hydraulic fractures [2]. Therefore, understanding hydraulic fracture behavior and its interaction with pre- existing fractures are essential to stimulate fractured reservoirs in a safe and responsible way, reducing the associated environmental risks. Several experimental works and field observations have been con- ducted to investigate the interaction between hydraulic and natural fractures [3–9]. Based on experiments, Blanton showed that a hydraulic fracture crosses a natural fracture under high differential stresses and high intercepting angles [4]. Since experimental models are expensive and extremely time consuming, recent researches have focused on the development of analytical and numerical algorithms to model hydraulic fracture propagation in fractured reservoirs[10–12]. Numerical techniques such as the discrete element method - DEM [13–15], the displacement discontinuity method -DDM [16–18] and the embedded fracture model -EFM [19] are viable alternatives to simulate the in- teraction between hydraulic and natural fractures. However, those methods generally consider linear elastic behavior and impermeable rock. In the finite element method - FEM, several studies adopt coupled interface elements [20–25] to simulate discontinuities with predefined paths. The extended finite element method - XFEM is more suitable for fracture propagation with arbitrary paths [11,26–30]. Recent works present an improvement of the XFEM method for hydraulic fracture propagation through a porous medium with multiple pre-existing nat- ural fractures [31,32]. However, the estimation of a coherent fracture propagation path using XFEM requires the definition of a suitable cri- terion for fracture initiation and propagation [33]. Furthermore, this method has some limitations due to the complexity of treatment of fracture interaction even in 2D cases. Among 3D models, Haddad et al. [22] performed a numerical in- vestigation to simulate the interaction of hydraulic and vertical natural fractures using a coupled interface element. To ensure fluid continuity https://doi.org/10.1016/j.compgeo.2020.103528 Received 14 October 2019; Received in revised form 27 February 2020; Accepted 28 February 2020 ⁎ Corresponding author. E-mail addresses: crisms@tecgraf.puc-rio.br (E.C. Mejia Sanchez), julioa@tecgraf.puc-rio.br (J.A. Rueda Cordero), deane@tecgraf.puc-rio.br (D. Roehl). Computers and Geotechnics 122 (2020) 103528 0266-352X/ © 2020 Published by Elsevier Ltd. T