Speaker
Description
May the H₂ Forces Be with You: Dimensionless Force Balance and Recovery Efficiency in Subsurface Hydrogen Storage
Objectives/Scope:
This paper aims to evaluate the dynamic interplay of capillary, viscous, and gravitational forces in hydrogen (H₂) geological storage and how these differ from other injected gases such as carbon dioxide (CO₂) and methane (CH₄). It focuses on identifying dominant flow regimes—using pore-scale and macroscopic capillary numbers and Bond numbers—and explores how these influence phase trapping, displacement efficiency, and overall storage security and recovery.
Methods, Procedures, Process:
We analyze H₂/H₂O/rock interactions across a range of flow regimes—capillary-dominated, transition, and viscous—using force-balance dimensionless numbers: capillary number (Nc), viscous-capillary number (Ncv), and Bond number (Nb). These numbers were applied to compare H₂ flow characteristics against CO₂ and CH₄ using theoretical models and literature-derived petrophysical data. Fluid properties such as density, viscosity, solubility, and diffusion coefficients were benchmarked to understand their impact on displacement behavior, phase mobility, and residual trapping. Sensitivity analyses on pore structure and flow rates were conducted to map transitions between force-dominant regimes. Special attention was given to how H₂’s low density, high diffusivity, and low viscosity modify the capillary and viscous balance under realistic subsurface conditions.
Results, Observations, Conclusions:
Hydrogen’s unique thermophysical properties yield a lower capillary number and higher mobility compared to CO₂ and CH₄, predisposing it to viscous fingering and lower trapping efficiency. In capillary-dominated regimes, H₂ demonstrates limited trapping due to poor resistance to capillary thresholds, resulting in early breakthrough and low recovery. As the Bond number increases, gravitational segregation can aid vertical displacement but may lead to stratification, especially in heterogeneous reservoirs. Conversely, viscous-dominated injection improves phase displacement but risks instability when Ncv and mobility ratios are high. Compared to CO₂, which benefits from higher solubility and density-driven stability, H₂ presents more challenges in achieving long-term containment due to its fast diffusion and weak interfacial forces. The findings indicate that optimal H₂ storage requires engineered flow conditions that minimize unfavorable fingering while maximizing capillary trapping, possibly through pulsed or staged injection.
Novel/Additive Information:
This paper introduces a comparative force-dynamics framework tailored for H₂ storage, integrating capillary, viscous, and gravitational mechanisms via dimensionless numbers. It offers novel insights into how fluid properties dictate dominant flow regimes and recovery efficiency, highlighting the need for customized injection strategies for effective and secure hydrogen storage—knowledge critical for advancing underground hydrogen storage as a viable energy transition technology.
| Country | Saudi Arabia |
|---|---|
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