4D X-ray Imaging Reveals Gas Mixing Dynamics in Porous Media
A study demonstrates the complexities of gas mixing in porous media using 4D X-ray imaging, challenging traditional models.
A recent study published in the Proceedings of the National Academy of Sciences investigates gas mixing in porous media, focusing on nitrogen injection into a porous sandstone saturated with krypton and water. The research employs 4D X-ray imaging to capture the evolution of gas mixture composition and the multiphase flow of gas and water.
Gas Connectivity and Composition Variance
The findings reveal that gas mixing does not follow the smooth, continuous patterns predicted by conventional advection–diffusion models. Instead, it evolves through distinct regimes influenced by gas connectivity. Initially, immiscible gas–water displacement creates variance in gas composition as different gases occupy adjacent pores separated by water. As gas connectivity improves, intermittent gas–liquid interfacial rearrangements rapidly link regions with differing gas compositions, leading to a swift reduction in composition variance.
Confined Diffusion and Ostwald Ripening
Once connectivity stabilizes, the mixing process transitions to a confined diffusion mechanism within the quasi-static gas network. Over time, further mixing occurs slowly through multicomponent Ostwald ripening, where trapped gas ganglia exchange solutes with the surrounding liquid phase. These insights enhance the understanding of gas mixing in porous media and propose new concepts for scaling up pore scale multiphase flow in subsurface gas mixing.
