Speaker
Description
Shale formations are recognized as an essential source of unconventional hydrocarbons, with kerogen, the embedded carbonaceous porous material, being the dominant source of valuable organic components. The unique nanostructure of kerogen, coupled with its inherent complexity, presents a significant challenge to unraveling the behavior of confined fluids and interactions within shale formations. Molecular modelling is the only available tool to explore the properties of kerogen at the atomic level. Compared to computationally intensive fully atomistic simulations, coarse-grained (CG) simulations provide a unique way to explore large kerogen structures of up to 1 million atoms with unprecedented detail and complexity within the microsecond scale. This work presents our recent advances in utilizing CG models to simulate kerogen structures encountered in shale formations. We discuss a strategy employed to build kerogen models, focusing on their structural representation, force field, and validation against experimental data.
Chemically-accurate CG models of different types of kerogen were constructed following a two-step process by a mimetic approach that obtains a kerogen slab from cross-linking kerogen units. We postulate that kerogen structures can be represented as a combination of aliphatic and aromatic molecular units such as n-dodecane, triphenylene, benzopyrene, perylene, and coronene [1]. By combining these molecules and adopting the SAFT force field [2] for their CG models, we generated models for four types of kerogens of different maturity including 1A, 2B, and 2D. To generate a kerogen slab, randomly chosen kerogen units were placed in a simulation box and allowed to artificially cross-link. Each of the constructed kerogen models reproduces the analytically-determined elemental composition of kerogen including H/C ratio and average aromaticity or the ratio of aromatic carbons to the total number of carbon atoms.
The developed CG models successfully capture essential features of kerogen such as the experimental density of organic matter, compressibility, dynamic swelling, and diffusion of confined fluids. In contrast to atomistic simulations, these CG models offer a unique platform for studying the effects of different gas and oil production techniques, storage of carbon dioxide, hydrogen, and separation of organic liquids under mild and extreme conditions.
References
1. 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.
2. 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.
