Numerical Modelling of Pore-Scale Multiphase Flow and Capillary Trapping of Supercritical CO2 in Subsurface Geological Formations

Numerical Modelling of Pore-Scale Multiphase Flow and Capillary Trapping of Supercritical CO₂ in Subsurface Geological Formations

 

Pore-scale numerical simulations can also be an effective tool to understand how pore geometry interacts with capillary and viscous forces to determine multi-fluid flow phenomena and capillary trapping. Although pore-network models have a long history in multi-phase flow simulation, recent efforts have focused on the lattice Boltzmann method (LBM) which is capable of reproducing realistic pore space geometry. Most existing LBM formulations suffer from numerical instabilities for low capillary numbers, and for high density and viscosity ratios – conditions essential for simulation of supercritical CO₂-brine systems. Recently, we developed an improved LBM for immiscible two-phase flow with variable viscosity and density ratios [1]. Some very recent results are shown below in Figure 1, where we simulate microfluidic experiments reported recently by [2]. Supercritical CO₂ (indicated in red) is injected from the left and displaces brine (indicated in blue). Advancement of CO₂ into the two different pore structures, and the extent and behaviour of CO₂ preferential flow (i.e., fingering), was found to depend on Capillary number, and the overall fingering patterns observed in the experiments were re-produced in the simulations.

Figure 1 Final fluid distribution in the dual-permeability microfluidic system at various capillary numbers. Note that the non-wetting LCO₂ and the wetting water are shown in red and blue colours, respectively.

This research will aim to integrate our pore-scale modelling efforts with experimental investigations being conducted at University of Illinois at Urbana-Champaign (UIUC), USA, to understand the physics of multiphase flow of brine and CO₂. In particular, we will focus on capillary trapping of residual CO₂ by flowing brine. We will benchmark our model by comparing with experiments currently being conducted by Prof Ken Christensen and Prof Albert J. Valocchi at UIUC as part of the I2CNER efforts. Although we have compared our model with multi-phase flow experiments in 2D micro-fluidic flow cells (see Figure 1), this research will permit validation with UIUC’s unique 3D experiments that will measure velocity as well as fluid configuration. The validated model will be used to investigate a variety of fluid characteristics (e.g., interfacial tension, viscosity, density) and a limited range of pore geometries. Another goal of this research is to further develop our suite of LBM codes to include miscibility of the CO₂-brine system; this will allow assessment of long-term solubility trapping and enhance understanding of the coupling between fingering processes and dissolution which occurs at the CO₂-brine interface.

References

For more information about the project contact Dr Haihu Liu (haihu.liu@strath.ac.uk), Lecturer at the Department of Mechanical and Aerospace Engineering at the University of Strathclyde.

 

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