Research

We are currently working on:

• Icy porous materials, specifically:
  • hydrates/ice-bearing sediments: predicting the fate of frozen methane and water in marine sediments and permafrost under climate warming or man-made perturbations.
  • snow/firn hydrology: understanding the fate of water in warming cryosphere to decide how we as a society should preserve and adapt.
• Geologic carbon sequestration: improving our engineered capability to safely store CO₂ underground away from the atmosphere.
• Subsurface biogeochemical processes: understanding and modeling the generation of greenhouse gases in soil and its subsequent exchange in the global carbon cycle.
• Geothermal systems: understanding, modeling and engineering fluid-rock interactions to enable efficient extraction of heat from subsurface.

Below you can learn more about some of the topics we have been exploring extensively.

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Methane hydrate is an ice-like solid that forms out of an aqueous solution of water and dissolved methane under moderate pressure and low temperature conditions. It is most commonly found in deep marine settings (>600m water depth) and permafrost regions on Earth . A large body of work over the past few decades has established a fundamental understanding of methane hydrate equilibrium thermodynamics. However, modeling nonequilibrium behaviors in hydrates remains challenging.

In this series work, we first develop a continuum-scale phase-field model to study gas–liquid–hydrate systems far from thermodynamic equilibrium. This modeling framework, in combination of a series of high-pressure microfluidic experiments, has then allowed us to study the nonequilbrium mechanics of gas percolation through the porous sediment under hydrate-forming conditions.

We uncover a phenomenon, which we call crustal fingering, that helps explain how, counterintuitively, hydrate formation may facilitate instead of prevent methane gas migration through deep ocean sediments.

Click here for a quick overview of gas hydrates in nature and some of the ways we study them in the field and in the lab.

• Crustal fingering facilitates free-gas methane migration through the hydrate stability zone; X. Fu*, J. Jimenez-Martinez*, T. P. Nguyen, J. W. Carey, H. Viswanathan, L. Cueto-Felgueroso, and R. Juanes, Proceedings of the National Academy of Sciences, (2020)
  * Equal contribution
• Xenon hydrate as an analogue of methane hydrate in geologic systems out of thermodynamic equilibrium; X. Fu, W. F. Waite, L. Cueto-Felgueroso and R. Juanes; accepted in Geochem. Geophys. Geosyst. (2019).
• Nonequilibrium thermodynamics of hydrate growth on gas–liquid interface; X. Fu, L. Cueto-Felgueroso, R. Juanes; Phys. Rev. Lett.,120(14):144501 (2018); [pdf]
  * Editor's suggestion
• Laboratory observations of the evolution and rise rate of bubbles with and without hydrate shells; W. F. Waite, T. Weber, X. Fu, R. Juanes, C. Ruppel; Proceedings of the 9th ICGH (2017);

In this series work, we study the evolution of binary mixtures far from equilibrium, and show that the interplay between phase separation and hydrodynamic instabilities in porous media give rise to new nonequilibrium phenomena. Specifically, we show that:

• viscously unstable flow can arrest the Ostwald ripening process characteristic of non-flowing mixture;
  • Thermodynamic coarsening arrested by viscous fingering in partially miscible binary mixtures; X. Fu, L. Cueto-Felgueroso, R. Juanes; Physical Review E, 94(3),033111(5) (2016); [pdf][video1][video2]​
• fluid-fluid partial miscibility exerts a powerful control on the degree of viscous fingering;
  • Viscous fingering with partially miscible fluids; X. Fu, L. Cueto-Felgueroso, R. Juanes; Phys. Rev. Fluids, 2(10):104001 (2017); [pdf]​
• pore-scale wettability and microstructure influences the morphology and dynamics of evaporative gas flow.
  • Pore-scale modeling of phase change in porous media; L. Cueto-Felgueroso, X. Fu, R. Juanes; Physical Review Fluids, 3, 084302 (2018). [pdf]

Geologic carbon dioxide sequestration entails capturing and injecting CO2 into deep saline aquifers for long-term storage. The injected CO2 mixes with groundwater, forming a mixture that is denser than the initial groundwater. The local increase in density triggers a gravitational instability at the boundary layer that further develops into columnar plumes of CO2-rich brine, a process that is referred to as convective mixing and greatly accelerates solubility trapping of CO2. Here, we investigate the pattern-formation aspects of convective mixing along with rock-altering reactions during geological CO2 sequestration by means of high-resolution three-dimensional simulations and analogue laboratory experiments.

• Dissolution patterns from geochemical reactions during convection mixing in porous media; X. Fu, L. Cueto-Felgueroso, D. Bolster, R. Juanes; Journal of Fluid Mechanics, 764:296-315 (2015); [pdf]
• ​Pattern formation and coarsening dynamics in three-dimensional convective mixing in porous media; X. Fu, L. Cueto-Felgueroso, R. Juanes; Philosophical Transactions of the Royal Society A, 371:20120355 (2013); [pdf][videos]