(615e) Probing the Relationships between the Pore Nanostructure of Kerogen and the Transport Behavior of Confined Hydrocarbons Using a Coarse-Grained Model

Kerogen is an intrinsically complex, heterogeneous, and disordered material [1]. Depending on its geological origin and maturity, the chemical composition of kerogen may vary significantly along with its structural properties, such as the density of the network and its intrinsic porosity [2]. Furthermore, upon hydrocarbon migration in shales, extraction, and adsorption, the cross-linked networks dynamically change, making the experimental and modelling of this porous media very challenging.

This work presents recent advances in utilizing molecular dynamics (MD) simulations to explore the adsorption and transport of high-pressure light and heavy hydrocarbons such as methane, toluene, cyclohexane, and n-decane and their impact on the dynamic behavior of a kerogen nanostructure. Kerogen structures are developed following a mimetic algorithm using chemically-accurate coarse-grained models. We postulate that kerogen structures can be assembled as a combination of aliphatic and aromatic molecular building blocks such as n-dodecane, triphenylene, benzopyrene, perylene, and coronene [3]. Combining these molecules and adopting the SAFT force field [4] for their coarse-grained models, we generate fully cross-linked structures representative of two types of kerogens of different maturity, including 1A and 2B. The models are validated against available experimental data and in-silico data [3]. The developed CG models offer a unique platform for studying thermodynamic and transport properties of hydrocarbon fluids.

The simulation results show that the adsorption of hydrocarbons induces swelling of kerogens. We determined that swelling with liquid hydrocarbons induces changes in interconnected and highly microporous structures with a high surface area, and an average pore diameter of ~6 Å. Using equilibrium MD simulations, we explored the self-diffusion of confined solvents. Moreover, the pathways formed due to kerogen swelling allowed us to determine transport diffusion of liquid hydrocarbons utilizing boundary-driven non-equilibrium MD simulations. The developed coarse-grained models provide important insights into establishing the relationships between the complex nanostructure of the pore network and transport behavior of hydrocarbons confined in kerogen. Understanding these relationships helps the development of enhanced oil recovery processes.

References:

1. E. Rezlerová, S. K. Jain, M. Lísal, Adsorption, Diffusion, and Transport of C1 to C3 Alkanes and Carbon Dioxide in Dual-Porosity Kerogens: Insights from Molecular Simulations, Energy Fuels, 37, 492-508, 2023.
2. D. Ertas, S. R. Kelemen, T. C. Halsey, Petroleum Expulsion Part 1. Theory of Kerogen Swelling in Multicomponent Solvents, Energy & Fuels, 20, 295-300, 2006.
3. P. Ungerer, J. Collell, M. Yiannourakou, Molecular Modeling of the Volumetric and Thermodynamic Properties of Kerogen: Influence of Organic Type and Maturity, Energy Fuels, 29(1), 91-105, 2015.
4. E. A. Müller and G. Jackson, Force-Field Parameters from the SAFT-γ Equation of State for Use in Coarse-Grained Molecular Simulations, Annu. Rev. Chem. Biomolec. Eng., 5, 405-427, 2014.