Chemistry and Dynamics of Supercritical Carbon Dioxide and Methane in the Slit Pores of Layered Silicates

Geoffrey M Bowers; Narasimhan Loganathan; John S Loring; Herbert Todd Schaef; A Ozgur Yazaydin

doi:10.1021/acs.accounts.3c00188

Chemistry and Dynamics of Supercritical Carbon Dioxide and Methane in the Slit Pores of Layered Silicates

Acc Chem Res. 2023 Jul 4;56(13):1862-1871. doi: 10.1021/acs.accounts.3c00188. Epub 2023 Jun 20.

Authors

Geoffrey M Bowers¹, Narasimhan Loganathan², John S Loring³, Herbert Todd Schaef³, A Ozgur Yazaydin⁴

Affiliations

¹ Department of Chemistry and Biochemistry, St. Mary's College of Maryland, 47645 College Drive, St. Mary's City, Maryland 20686, United States.
² Department of Chemistry, Michigan State University, 578 South Shaw Lane, East Lansing, Michigan 48824, United States.
³ Computational and Molecular Sciences Directorate, Pacific Northwest National Laboratory, 3335 Innovation Boulevard, Richland, Washington 99352, United States.
⁴ Department of Chemical Engineering, University College London, London, U.K. WC1E 7JE.

PMID: 37339149
DOI: 10.1021/acs.accounts.3c00188

Abstract

ConspectusIn the mid 2010s, high-pressure diffraction and spectroscopic tools opened a window into the molecular-scale behavior of fluids under the conditions of many CO₂ sequestration and shale/tight gas reservoirs, conditions where CO₂ and CH₄ are present as variably wet supercritical fluids. Integrating high-pressure spectroscopy and diffraction with molecular modeling has revealed much about the ways that supercritical CO₂ and CH₄ behave in reservoir components, particularly in the slit-shaped micro- and mesopores of layered silicates (phyllosilicates) abundant in caprocks and shales. This Account summarizes how supercritical CO₂ and CH₄ behave in the slit pores of swelling phyllosilicates as functions of the H₂O activity, framework structural features, and charge-balancing cation properties at 90 bar and 323 K, conditions similar to a reservoir at ∼1 km depth. Slit pores containing cations with large radii, low hydration energy, and large polarizability readily interact with CO₂, allowing CO₂ and H₂O to adsorb and coexist in these interlayer pores over a wide range of fluid humidities. In contrast, cations with small radii, high hydration energy, and low polarizability weakly interact with CO₂, leading to reduced CO₂ uptake and a tendency to exclude CO₂ from interlayers when H₂O is abundant. The reorientation dynamics of confined CO₂ depends on the interlayer pore height, which is strongly influenced by the cation properties, framework properties, and fluid humidity. The silicate structural framework also influences CO₂ uptake and behavior; for example, smectites with increasing F-for-OH substitution in the framework take up greater quantities of CO₂. Reactions that trap CO₂ in carbonate phases have been observed in thin H₂O films near smectite surfaces, including a dissolution-reprecipitation mechanism when the edge surface area is large and an ion exchange-precipitation mechanism when the interlayer cation can form a highly insoluble carbonate. In contrast, supercritical CH₄ does not readily associate with cations, does not react with smectites, and is only incorporated into interlayer slit mesopores when (i) the pore has a z-dimension large enough to accommodate CH₄, (ii) the smectite has low charge, and (iii) the H₂O activity is low. The adsorption and displacement of CH₄ by CO₂ and vice versa have been studied on the molecular scale in one shale, but opportunities remain to examine behavioral details in this more complicated, slit-pore inclusive system.