Supercritical CO₂ and CH₄ Uptake by Illite-Smectite Clay Minerals

Area of Science:

• Geochemistry
• Materials Science
• Energy Science

Background:

• Clay minerals are abundant in sedimentary rocks and influence geoenergy applications through gas interactions.
• Quantifying gas uptake in clays is essential for understanding storage capacity and gas recovery.

Purpose of the Study:

• To systematically investigate the sorption properties of three distinct clay minerals (montmorillonite, illite-smectite, illite) for carbon dioxide (CO2) and methane (CH4).
• To assess the impact of clay pore structure and temperature on gas adsorption up to 30 MPa.
• To validate a lattice density functional theory model for predicting gas adsorption in clay-bearing formations.

Main Methods:

• Gas physisorption using N2 and Ar for textural characterization.
• Supercritical excess sorption experiments with CO2 and CH4 at varying pressures and temperatures.
• Lattice density functional theory modeling calibrated with experimental data.

Main Results:

• Micropore accessibility varied between clay types and probe gases (N2, Ar, CO2).
• CO2 uptake was higher in illite-rich samples, influenced by clay-specific pore size distributions.
• The density functional theory model accurately described measured sorption isotherms and isosteric heats of adsorption.

Conclusions:

• Gas adsorption in clay minerals is governed by pore size distribution and temperature.
• The developed model demonstrates predictive capability for gas adsorption in geological formations.
• Maximum pore occupancy is temperature-dependent, approaching unity near the critical temperature for both gases and clays.