Speaker
Description
In carbon capture and storage (CCS), CO₂ injection behavior in porous media is governed not only by injection rate and fluid composition but also by the interaction between injection strategy and pore-network structure, leading to inherently nonlinear displacement dynamics at the pore scale. In this study, we used a physical rock micromodel CO₂ displacement under continuous injection and surfactant-alternating-gas (SAG) injection through quantitative metrics and image-based analysis.
Continuous-injection tests were conducted over 0.001–0.1 mL/min, whereas SAG tests were performed over 0.005–0.5 mL/min with 0.5–2 injected pore volumes (PV). Experiments were carried out at NaCl concentrations of 0 M and 0.599 M using aqueous solutions of SDBS (0.01 wt%) and Glucopon (0.01 wt%). Under continuous injection, displacement efficiency increased with injection rate for both surfactant systems. At NaCl 0 M, efficiency in the SDBS system increased from 45.7% at 0.001 mL/min to 76.2% at 0.1 mL/min, while the Glucopon system increased from 59.1% to 78.0% over the same rate range. At NaCl 0.599 M, the Glucopon system reached approximately 81% efficiency at 0.1 mL/min. Image observations showed comparatively stable and continuous displacement fronts at higher injection rates for both systems.
In contrast, SAG injection did not produce a monotonic dependence of efficiency on injected PV. For example, at NaCl 0 M in the SDBS system at 0.05 mL/min, continuous injection yielded an efficiency of approximately 78.8%, whereas SAG efficiencies at 0.5 PV, 1 PV, and 2 PV were 56.4%, 61.0%, and 58.3%, respectively, demonstrating non-monotonic fluctuations with alternating injection. Pore-scale images further indicated repeated pathway reconfiguration during phase switching, including simultaneous disconnection of established flow paths and localized invasion into previously unoccupied pore bodies.
Image-based pore-network analysis showed that the micromodel exhibits a structurally constrained network, with an average pore-body connectivity of approximately 3–4 and many pore bodies connected through a limited number of throats. During SAG, CO₂ invasion preferentially occurred through relatively well-connected pore bodies and larger throats, whereas low-connectivity pore bodies were repeatedly bypassed or became locally isolated. As a result, increasing injected PV altered the spatial distribution of invaded regions but did not drive the overall efficiency toward a single direction or convergence.
In the Glucopon system, continuous injection already produced reduced fingering and a relatively uniform front, and the additional impact of SAG on pore-scale pathways was limited. Under SAG at 0.05 mL/min, efficiencies were in the range of approximately 54–59%, without a clear improvement relative to the continuous-injection case. These results indicate that the influence of alternating injection is governed less by injected PV or surfactant identity per se than by the degree of residual capillary control established under continuous injection and by connectivity- and throat-size–controlled accessibility within the pore network.
Overall, our results provide quantitative and image-based evidence that non-steady injection strategies can reconfigure pore-scale pathway selection in structurally constrained porous media, but the resulting displacement response is non-monotonic and strongly condition-dependent. This highlights the need to interpret SAG and related strategies from a pore-scale flow-mechanism perspective rather than relying solely on efficiency-based performance metrics.
| Country | Republic of Korea (South Korea) |
|---|---|
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