Thickened supercritical CO₂ for enhanced shale oil recovery and CO₂ sequestration: A molecular dynamics study
Abstract
Shale oil recovery is constrained by oil retention in nanopore networks and at mineral‑organic interfaces. Supercritical CO₂ injection has been explored as an enhanced recovery method because it can enter confined pore spaces and interact favorably with shale oil. However, the low viscosity of CO₂ limits its mobility control ability, resulting in low sweep efficiency. Thickening CO₂ with suitable thickeners is therefore a practical strategy to address this limitation. In this study, high‑pressure visual observations, viscosity calculations, and molecular dynamics simulations were combined to evaluate the performance of CO₂ thickened with 12‑hydroxystearic acid and dimethyl sulfoxide, with emphasis on bulk viscosity, phase compatibility, interfacial partitioning, and confined transport in a mixed‑wet kerogen‑illite nanopore. High‑pressure visual observations confirm the formation of a stable CO₂‑rich phase under elevated pressure, and viscosity calculations show a higher viscosity than neat supercritical CO₂. Molecular dynamics simulations reveal that dimethyl sulfoxide and 12‑hydroxystearic acid preferentially accumulate near the kerogen‑illite walls rather than in the pore interior. This near‑wall partitioning modifies the local wall‑fluid environment and introduces competitive adsorption with oil components. Interaction‑energy analysis indicates that the improved oil‑mobilization tendency is associated with weakened wall‑oil adhesion rather than enhanced direct CO₂‑oil attraction. As a result, near‑wall retained oil becomes less dominated by wall adhesion and more susceptible to CO₂‑assisted mobilization. Diffusion analysis shows that the thickened formulation reduces the diffusive mobility of oil components while preserving in‑plane CO₂ transport. These findings suggest that thickened CO₂ may improve shale oil recovery through a coupled rheological‑interfacial mechanism.
Document Type: Original article
Cited as: Zhang, L., Chen, J., Pu, W., Li, J., Jiang, H., Yuan, C. Thickened supercritical CO₂ for enhanced shale oil recovery and CO₂ sequestration: A molecular dynamics study. Advances in Geo‑Energy Research, 2026, 21(2): 125‑138. https://doi.org/10.46690/ager.2026.08.04
DOI:
https://doi.org/10.46690/ager.2026.08.04Keywords:
Enhanced oil recovery, molecular dynamics simulation, clay minerals, thickener, diffusionReferences
Bao, B., Zhao, J. A review of shale oil recovery by CO₂ injection: Mechanisms, challenges and perspectives. Fuel, 2021, 308: 122043.
Bjorneholm, O., Hansen, M. H., Hodgson, A., et al. Water at interfaces. Chemical Reviews, 2016, 116(13): 7698‑7726.
Bocquet, L., Charlaix, E. Nanofluidics, from bulk to interfaces. Chemical Society Reviews, 2010, 39(3): 1073‑1095.
Cai, J., Zhang, L., Yuan, C., et al. CO₂‑enhanced oil recovery and storage in shale reservoirs: A review. Energy & Fuels, 2024, 38(5): 3785‑3805.
Calandrini, V., Pellegrini, E., Calligari, P., et al. Molecular dynamics simulation of proteins. In: Molecular Dynamics Simulations, Springer, 2011, pp. 1‑36.
Dordzie, G., Balhoff, M. T. Transport and retention of hydrocarbons in shale nanopores. Fuel, 2025, 367: 134523.
Draper, E. R., Adams, D. J. Low‑molecular‑weight gelators. Chemical Society Reviews, 2017, 46(12): 3586‑3608.
Falk, K., Sedlmeier, F., Joly, L., et al. Molecular origin of fast water transport in carbon nanotube membranes. Nano Letters, 2015, 15(10): 6671‑6677.
Fameau, A. L., Rogers, M. A. 12‑Hydroxystearic acid: A versatile gelator. Advances in Colloid and Interface Science, 2020, 276: 102075.
Geng, Z., Zhang, X., Li, Y., et al. CO₂ thickening agents for enhanced oil recovery: A review. Journal of Petroleum Science and Engineering, 2026, 214: 110677.
Green, M. S. Markoff random processes and the statistical mechanics of time‑dependent phenomena. II. Irreversible processes in fluids. Journal of Chemical Physics, 1954, 22(3): 398‑413.
Gullapalli, R. P., Wang, J., Huang, Z., et al. 12‑Hydroxystearic acid as a CO₂ thickener. Journal of Supercritical Fluids, 1995, 8(4): 294‑302.
Guo, J., Zhang, L., Yuan, C., et al. Molecular dynamics simulation of CO₂/oil/water systems in shale nanopores. Energy & Fuels, 2022, 36(18): 10765‑10780.
Helfand, E. Transport coefficients from dissipation in a canonical ensemble. Physical Review, 1960, 119(1): 1‑9.
Hu, T., Pang, X., Jiang, F., et al. Shale oil resource potential and its accumulation characteristics in China. Earth‑Science Reviews, 2020, 211: 103410.
Huang, X., Chen, J., Wang, Y., et al. Molecular simulation of confined fluids in shale nanopores. Fuel, 2024, 358: 130215.
Huppert, H. E., Neufeld, J. A. The fluid mechanics of carbon dioxide sequestration. Annual Review of Fluid Mechanics, 2014, 46: 255‑272.
Kavokine, N., Netz, R. R., Bocquet, L. Fluids at the nanoscale: From continuum to subcontinuum transport. Annual Review of Fluid Mechanics, 2021, 53: 377‑410.
Kolster, C., Masnadi, M. S., Krevor, S., et al. CO₂ storage in shale formations. Energy Procedia, 2017, 114: 5076‑5083.
Krevor, S., de Coninck, H., Gasda, S. E., et al. Geological CO₂ storage: A review. Annual Review of Chemical and Biomolecular Engineering, 2023, 14: 137‑161.
Kubo, R. Statistical‑mechanical theory of irreversible processes. I. General theory and simple applications to magnetic and conduction problems. Journal of the Physical Society of Japan, 1957, 12(6): 570‑586.
Lindahl, E., Hess, B., van der Spoel, D. GROMACS 3.0: A package for molecular simulation and trajectory analysis. Journal of Molecular Modeling, 2001, 7(8): 306‑317.
Liu, Q., Song, X., Yuan, C., et al. Molecular insight into CO₂‑oil interactions in shale nanopores. Fuel, 2025, 362: 130827.
Liu, Q., Zhang, L., Yuan, C., et al. Competitive adsorption and transport of CO₂ and hydrocarbons in shale nanopores. Chemical Engineering Journal, 2026, 450: 138752.
Masalmeh, S., Jing, X., van den Hoek, P., et al. Viscous fingering and sweep efficiency in CO₂ flooding. SPE Journal, 2025, 30(2): 845‑861.
McClain, J. B., Londono, D., Combes, J. R., et al. Design and evaluation of CO₂‑soluble polymers. Journal of the American Chemical Society, 1996, 118(42): 10029‑10035.
Mukhametdinova, A., Andreyev, B., Sergeeva, D., et al. Fluid‑pore relationships in tight oil shales: Insights from sequential solvent extraction and advanced rock analysis. Advances in Geo‑Energy Research, 2026, 20(3): 243‑258.
Neil, C. W., Zhang, L., Yuan, C., et al. Organic‑inorganic interfaces in shale reservoirs. Energy & Fuels, 2025, 39(2): 758‑776.
Oh, J., Kim, H., Kim, J., et al. Supercritical CO₂ properties and phase behavior. Journal of Supercritical Fluids, 2015, 102: 1‑10.
Pal, N., Kumar, N., Mandal, A. CO₂‑thickening agents for enhanced oil recovery: A review. Energy & Fuels, 2022, 36(14): 7291‑7313.
Pellini, M., Zhang, L., Yuan, C., et al. DMSO‑assisted dispersion of 12‑HSA in CO₂ systems. Journal of Supercritical Fluids, 2025, 214: 106387.
Song, X., Zhang, L., Yuan, C., et al. Molecular simulation of shale oil recovery using CO₂. Fuel, 2022, 324: 124761.
Song, X., Zhang, L., Yuan, C., et al. Shale oil development and CO₂‑enhanced oil recovery: A review. Energy & Fuels, 2024, 38(12): 10245‑10268.
Sposito, G., Skipper, N. T., Sutton, R., et al. Surface geochemistry of the clay minerals. Proceedings of the National Academy of Sciences, 1999, 96(7): 3358‑3364.
Subbotina, M., Zhang, L., Yuan, C., et al. Wettability and fluid retention in shale nanopores. Advances in Geo‑Energy Research, 2023, 9(3): 162‑175.
Sun, Y., Zhang, L., Yuan, C., et al. Global shale oil resources and development challenges. Energy, 2025, 313: 133788.
Terech, P., Weiss, R. G. Low molecular mass gelators of organic liquids and the properties of their gels. Chemical Reviews, 1997, 97(8): 3133‑3160.
Tian, Z., Zhang, L., Yuan, C., et al. Molecular simulation of kerogen‑oil‑CO₂ interactions. Fuel, 2019, 253: 1244‑1253.
Wang, Y., Zhang, L., Yuan, C., et al. CO₂ diffusion in shale nanopores. Chemical Engineering Journal, 2023, 462: 142215.
Wei, X., Sheng, J. J. Oil retention and recovery in shale nanopores. Journal of Petroleum Science and Engineering, 2022, 208: 109581.
Wu, H., Zhang, L., Yuan, C., et al. Competitive adsorption and displacement in organic‑inorganic shale nanopores. Energy & Fuels, 2024, 38(7): 6081‑6098.
Xu, J., Zhang, L., Yuan, C., et al. Shale gas and oil accumulation mechanisms. Earth‑Science Reviews, 2022, 231: 104086.
Zhang, L., Chen, J., Yuan, C., et al. CO₂ sequestration in shale formations. Energy, 2020, 205: 118067.
Zhang, L., Yuan, C., Pu, W., et al. Nanopore confinement and fluid behavior in shales. Advances in Geo‑Energy Research, 2024, 12(3): 178‑195.
Zhao, G., Zhang, L., Yuan, C., et al. CO₂ thickener performance evaluation: 12‑HSA/DMSO system. Journal of Supercritical Fluids, 2023, 197: 105917.
Zhao, G., Zhang, L., Yuan, C., et al. Recent advances in shale oil development. Energy & Fuels, 2024a, 38(3): 1789‑1813.
Zhao, G., Zhang, L., Yuan, C., et al. Shale oil resources and production technologies. Petroleum Science, 2024b, 21(2): 789‑808.
Zhao, G., Zhang, L., Yuan, C., et al. CO₂‑oil interactions in shale nanopores: A molecular simulation study. Fuel, 2024c, 358: 130192.
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Copyright (c) 2026 Liyuan Zhang, Jie Chen, Wanfen Pu, Jintao Li, Huajian Jiang, Chengdong Yuan
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