Speaker
Description
In this study, we conducted a series of microfluidic experiments using Stereolithography (SLA) 3D-printed chips designed to replicate the pore geometry of vesicular basalts and investigate a scaled version of in-situ supercritical CO₂ (scCO₂)/water/basalt multiphase flow dynamics under room conditions and a large parameter space. Multiple field-scale pilot projects, such as those conducted at Wallula and CarbFix, underscore the viability of sequestering scCO₂ in basaltic formations, specifically in the highly permeable flow-top vesicular zones. These zones are characterized by millimeter-sized vesicles connected through microfractures across basalt matrix and nanopores in clay, forming a dual-porosity system with a large aspect ratio that differs substantially from conventional sedimentary reservoirs. The transport of scCO₂ under in-situ conditions in basalt dual-porosity networks remains poorly understood, hindering accurate predictions of CO₂ migration and mineralization inside basaltic formations. To approximate these pore morphologies, each microfluidic chip features an interconnected channel network that mirrors the high-aspect-ratio pore structure and dual-porosity characteristics of vesicular flow-top basalts.
Based on a comprehensive screening of potential working fluids, we selected fluorinated hydrocarbons as the nonwetting phase and mixed silicone oil as the wetting phase, effectively preserving the high viscosity ratio and wettability conditions of in-situ scCO₂/water/basalt systems under room conditions. Wetting and non-wetting fluids are co-injected by a syringe pump at various controlled rates and volume ratios to represent a range of reservoir conditions (i.e., flow rate and saturation state) from near-wellbore to far-field region. Bubbles of non-wetting fluid are generated through a T-junction at the inlet with a uniform size distribution controlled by channel width and flow rate. The dynamic evolution of bubbles within the interconnected channel system, including snap-off and coalescence events, is traced in the acquired video. Pulses of wetting fluid loaded with different dyes and tracer particles are injected at intervals to visualize steady-state velocity field and preferential flow pathway of wetting phase. A pressure sensor is integrated at the inlet and outlet ports to measure the pressure differential across the chip, enabling the calculation of relative permeability of each phase under different flow regimes. These combined flow visualization and pressure measurements yielded critical insights into: (1) the feedback loop among CO₂ bubble size distribution, occurrence of snap-off/coalescence events, and relative permeability, (2) steady-state partial water saturation within both mobile and immobile fluids, and (3) the preferential flow pathways in dual-porosity pore systems analogous to vesicular basalts.
We posit that the presented microfluidic diagnostics will enable scalable insights into in-situ scCO₂ migration and phase distributions and, ultimately, mineralization behaviors within basaltic formations. Preliminary results suggest that flow rate and channel size distribution strongly influence local partial saturation, relative permeability, and preferential flow pathway of both fluids. Going forward, corresponding fluid dynamic simulations (e.g., LBM and PNM) will be established and benchmarked against the experiment results. This expanded approach aims to elucidate the interplay between fluid transport and dual-porosity nature from a scalable aspect, ultimately optimizing injection schemes for efficient and secure in-situ carbon mineralization in basaltic formations.
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