A Coupled Hydro-Mechanical Model for Simulation of Two-Phase Flow and Geomechanical Deformation in Naturally Fractured Porous Media

: This paper presents a coupled fluid flow and geomechanics model for analysis of two-phase flow and deformation behaviors in naturally fractured porous media. The discrete fracture model (DFM) is used to model two-phase fluid flow. The zero-thickness interface element method coupled with a modified Barton-Bandis’s constitutive model is applied to model the mechanical behavior of natural fractures. The finite volume (FVM) and finite element (FEM) methods are used for the discretization of flow and geomechanical equations, respectively. The coupled problem is iteratively solved using the fixed-stress splitting algorithm. Then the proposed model is applied to investigate the two-phase fluid flow in fractured porous media under various in-situ stress conditions. The results show that fracture aperture significantly increases as the differential stress increases due to shear dilation, which accordingly enhances the equivalent permeability of the fractured medium. Channelized flow is formed through the dilated fractures, which results in early water breakthrough and reduces the water sweep efficiency. This study illustrates the importance of shear dilation on two-phase flow behaviors in fractured porous media and highlights the necessity of considering shear dilation for accurate prediction of saturation distributions. The simulations also demonstrate the capacity of our model to capture the complex coupled behavior induced by the interaction between pore pressure and in-situ stress loadings. 1. INTRODUCTION Hydro-mechanical coupling in fractured media is an important issue in various engineering applications, such as oil and gas recovery (Moinfar et al. 2013; Yan et al. 2018), geothermal reservoirs (Pandey et al. 2017; Li et al. 2019), CO2 sequestration (Rutqvist et al. 2007; Cappa and Rutqvist 2011), and nuclear waste disposal (Nguyen and Selvadurai 1995; Yow and Hunt 2002). As the high-conductive flow channels and weak surfaces, fractures are often characterized by the rough surfaces, which could deform under the joint influence of normal closure and shear dilation. In particular, shear dilation may play a dominant role when rough fractures suffer certain shear displacement, which is believed to be able to significantly enhance the fracture permeability (Zhang et al. 2008).