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Description
High-resolution three-dimensional X-ray microtomography was employed to investigate the steady-state relative permeability and pore-scale flow behavior of hydrogen (H₂) and carbon dioxide (CO₂) in a water-wet reservoir carbonate rock under subsurface conditions. This study extends previous pore-scale investigations of gas distribution, connectivity, and rearrangement by directly quantifying relative permeability using a steady-state fractional flow approach while simultaneously imaging fluid configurations within the same pore system.
The experiment was conducted using a steady-state fractional flow methodology at a pressure of 8 MPa and a temperature of 50 °C, representative of subsurface reservoir conditions. Brine and gas were co-injected under capillary-dominated flow across a wide range of fractional flow states, from single-phase brine injection to gas-dominated flow. A contrast-enhanced brine was used to enable accurate phase identification, and three-dimensional images were acquired at steady state for each fractional flow condition. Relative permeability was calculated from measured pressure gradients and flow rates, while segmented images were analyzed to quantify phase saturation, pore occupancy, gas connectivity, ganglia size distribution, and capillary pressure derived from interfacial curvature.
The results reveal systematic differences in the relative permeability behavior of H₂ and CO₂. For both gases, gas relative permeability remained low over most of the fractional flow range, reflecting strong capillary control and limited gas mobility in the water-wet carbonate pore space. However, H₂ exhibited slightly higher gas mobility at low water fractional flow compared to CO₂, consistent with its lower density and viscosity.
Pore-scale imaging demonstrated that both gases preferentially occupied larger pores and throats during steady-state flow. Nevertheless, H₂ formed more connected gas pathways, whereas CO₂ was distributed in more stable but less connected configurations. Capillary pressure measurements derived from interfacial curvature were consistent with these observations, highlighting reduced remobilization of CO₂ relative to H₂.
These findings provide a direct pore-scale comparison of steady-state relative permeability and flow behavior of H₂ and CO₂ in carbonate rocks. The enhanced mobility and connectivity of H₂ support efficient gas withdrawal during cyclic underground hydrogen storage, while the reduced mobility of CO₂ are favorable for long-term geological sequestration. The results offer important pore-scale constraints for reservoir-scale simulations and contribute to the design and optimization of subsurface gas storage strategies relevant to energy transition and climate mitigation.
| Country | United Kingdom |
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