Pore-filling behaviors and lateral propagation of CH4 and CO2 hydrates forming in microfluidic porous media

Understanding in-pore hydrate growth and across-pore propagation is crucial for predicting flow and mechanical properties in CH₄ hydrate recovery and CO₂ sequestration. We developed a novel microfluidic technique to examine hydrate phase transitions at both individual and collective pore scales. Our study reveals density-dependent pore-filling behaviors, addressing gaps left by previous microfluidic studies. Hydrates formed from lighter phases, such as gaseous CH₄ and CO₂, partially fill pores by coating pore walls upon reaching equilibrium. In contrast, hydrates formed from denser phases, like liquid CO₂, rapidly cement the pores due to volume expansion, significantly reducing the permeability of the host material. This pore-filling phenomenon was verified using fluorescence imaging and analyzed through the volume variation index, with kinetics examined under various conditions. We uncovered intrinsic spatial stochasticity in hydrate formation within porous media, characterized by a random distribution of newly formed hydrates. This randomness can be mitigated through an injection process simulating CO₂ storage, which promotes directional hydrate propagation along pressure gradients. Lastly, we propose an alternating CO₂-water injection method to enhance CO₂ storage capacity and injectivity in shallow seabed environments.