Development of Multiphase Flow Simulation Method in DEM Under a Fixed-Grain Condition

Abstract

ABSTRACT Understanding multiphase flow mechanisms in porous media is vital for many engineering practices, such as geo-logical carbon sequestration. Existing numerical models that use the explicit pressure-solving scheme can only advance multiphase flow with a small timestep. None of them manages fast fluid transport due to a stability issue limiting timestep selection. This paper focuses on developing a fluid flow model that can quickly and efficiently capture fluid–fluid displacement patterns. We incorporate the implicit finite volume approach that is unconditionally stable to transport fluid with a remarkable timestep. To enhance interface–motion capture under various capillary number and viscosity ratio combinations, we set a flow front advancement criterion to reduce timestep when the injected fluid invades beyond front–line pores. Additionally, we update the flow front, pore pressure, and capillary entry pressure at every timestep to reveal more flow pattern details. We validate the model through a Darcy flow test and a fluid injection test based on existing Hele–Shaw tests. Numerical results agree well with the analytical solutions and experimental observations, confirming that the developed model is reliable for analyzing fluid migration problems and evaluating dynamic multiphase flow interactions in porous media. INTRODUCTION Geological CO2 sequestration is a crucial strategy for achieving carbon neutrality that stores greenhouse gas in geological formations, such as deep saline aquifers and depleted oil/gas reservoirs (Bradshaw et al., 2007; Bachu, 2008). Understanding how the injected CO2 migrates in geological media is vital to ensure successful CO2 geological storage. The injected CO2 will build up pore pressure and replace the existing pore fluid, remarkably altering the material properties (Sun et al., 2016) and pore structure (Yu et al., 2019). The pressure build-up during the injection process may trigger disasters, such as fault reactivation (White et al., 2014) and even earthquakes (Zoback and Gorelick, 2012), leading to CO2 leakage. To optimize CO2 injectivity and storage safety, it is thus essential to study multiphase flow mechanisms of fluid injection in porous media.