(587b) Methane Mass Transfer in Liquid Hydrocarbon Mixtures – Measurement and Modeling in Bulk and in Porous Media

Methane (CH₄) dissolution and mass transport in liquid hydrocarbon mixtures is of key interest in enhanced recovery from tight shales. In this project, we have studied CH₄ dissolution and mass transport in normal alkane mixtures, both in the bulk and when confined in model nanoporous silica media at subsurface relevant conditions. The objective here is to promote a better understanding of the impact of nanoconfinement on solubility and mass transfer.

For the measurement of CH₄ dissolution/diffusion in bulk liquid hydrocarbon mixtures, we utilized a high pressure and temperature, constant-volume diffusion set-up. We studied three different normal alkanes: Decane (C₁₀), dodecane (C₁₂) and hexadecane (C₁₆). We measured CH₄ dissolution and diffusion, at formation-relevant conditions, in its binary mixtures with the three normal alkanes, as well as in ternary and quaternary mixtures. During the experiments, the swelling of the liquid mixture due to CH₄ dissolution was measured in situ via a cathetometer, and was subsequently integrated into the data analysis. A key conclusion from this part of the study is that the thermodynamic and transport properties of the multicomponent mixtures can be well predicted from the binary mixture measurements via the use of an appropriate Equation of State (EOS) and the application of the classical Stefan-Maxwell (SM) diffusion theory. This observation facilitates accurate analysis and prediction for diffusive mass transfer in more complex liquid hydrocarbon mixtures.

To measure mass transfer in the alkane mixtures under nano-confinement, we employed a high pressure and temperature Wicke-Kallenbach diffusion cell. Measurements were performed for model porous materials, prepared from silica, with a narrow pore size distribution (~4 nm). The porous disks were impregnated with the alkane(s) and placed in-between the two half-cells of the setup. The top cell is pressurized with gaseous CH₄, while the liquid (pure or mixture) flows in the bottom cell. By monitoring the pressure drop in the top cell, we can infer the rate of dissolution and diffusion of CH₄ through the model porous silica. A direct comparison of the experimental observations with the bulk phase measurements, allows us to delineate the impact of nano-confinement on diffusive mass transfer.