Density-Dependent Pore-Filling Behaviors and Lateral Propagation of Ch4 and Co2 Hydrates Forming in Microfluidic Porous Media

Abstract

Understanding the dynamics of in-pore hydrate growth and across-pore hydrate propagation in porous media is essential for predicting the flow characteristics and mechanical properties of hydrate-bearing sediments in methane (CH4) hydrate recovery and carbon dioxide (CO2) sequestration. We developed a novel microfluidic technique that allows for the examination of hydrate phase transition behaviors at individual pores and collectively across thousands of pores, a capability not previously reported. Our study reveals density-dependent pore-filling behaviors during gas hydrate formation, addressing knowledge gaps left by earlier 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 visualized 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, demonstrating a random distribution of newly formed hydrates. This randomness can be mitigated through an injection process that simulates CO2 storage, promoting 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.

Keywords: CH4 hydrate, CO2 hydrate, Porous media, Microfluidics, Hydrate formation, pore-filling behaviors.