The effects of fluid characteristics in immiscible two-phase flow on migration and residual phenomena in heterogeneous pore networks

Geological CO2 sequestration (GCS) is one of the most promising technologies for mitigating greenhouse-gas emission into the atmosphere. In GCS operations, residual trapping is the most favorable form of trapping mechanism because of its storage security and capacity. This novel storage option for CO2 involves injecting supercritical CO2 (scCO2) into porous formations saturated with pore fluid such as brine and initiate CO2 flooding with immiscible displacement. Despite of significant effects on macroscopic migration and distribution of injected CO2, however, only a limited information is available on the effects of immiscible two-phase flow on dynamic phenomena in microscopic scCO2-brine-glass pore systems. In this study, the effects of hydrodynamic characteristics of two immiscible fluids - carbon dioxide in supercritical phase and porewater - and their interfaces on their migration and distribution patterns in heterogeneous pore networks are investigated. For the purpose, a series of injection experiments were performed using 2D transparent micromodels. The immiscible two-phase flow with displacement and residual phenomena during drainage processes in heterogeneous pore networks were visually observed using a high-resolution microscope and a camera, and the temporal and spatial changes in distribution and saturation of the two immiscible fluids were quantitatively estimated at the pore-scale using image processing. To compare with experimental results and to analyze the phenomena quantitatively, a series of numerical simulations are also carried out. A 2D phase field model is established in the COMSOL Multiphysics platform and is applied to simulate the two-phase flow and immiscible displacement phenomena during drainage processes in pore networks with varying major model parameters such as injection mass flow rates, contact angles, viscosity ratios etc. The experimental observations are used to validate the accuracy of the numerical model. The results from experimental observations and numerical simulations are in good agreement in migration and distribution patterns and can provide important fundamental information on hydrodynamic characteristics of immiscible two-phase flow at pore-scale in porous networks for geological CO2 sequestration.