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Multi-scale numerical modeling of radionuclides transport in sandy facies of the Opalinus Clay
首页 - 学术活动
首页 - 学术活动报告人：
Dr. Tao Yuan, Department of Geosciences, University of Tübingen, Germany
邀请人：
Chensong Zhang, Associate Professor
题目：
Multi-scale numerical modeling of radionuclides transport in sandy facies of the Opalinus Clay
时间地点：
19:30-20:30 October 12 (Wednesday), Tencent Meeting ID: 463-7874-0598
摘要：
Clay rock formations such as Opalinus Clay (OPA) are considered as host rocks for underground radioactive waste repositories. Molecular diffusion is an important transport mechanism for radionuclide migration in clay rock due to its very low hydraulic conductivity. Reliable predictions of diffusive transport heterogeneity are critical for assessing the sealing capacity of clay rocks. The predictive power of numerical approaches to flow field analysis and radionuclide migration depends on the quality of the underlying pore network geometry. Both sedimentary and diagenetic complexity in sandy facies are controlling factors.
In this talk, I will first introduce our recent study on a cross-scale approach to reconstruct the pore network geometries of the sandy facies of the Opalinus Clay (SF-OPA) rock1. The resulting generalized pore network geometries are applied in digital rock models to calculate effective diffusivities, using a combined upscaling workflow for transport simulations from nanometer to micrometer scales2. We further validate the simulation results via the Positron emission tomography (PET) diffusion experiments. Next, as a follow-up study, we investigate the influence of sedimentary and diagenetic heterogeneity on heterogeneous diffusion in SF-OPA from lamina scale to drill core scale3. Our numerical results based on the simplified structural model show fast diffusion fronts in clay laminae and slow diffusion fronts in carbonate lenses and sand laminae, demonstrating the endmembers of heterogeneous diffusion patterns in SF-OPA. The sensitivity studies show that the diffusion length and homogenization time increase by up to 190% when the length and thickness of the carbonate lenses are doubled. This study provides quantitative constraints on the temporal and spatial evolution of heterogeneous diffusion at the core scale.
At last, I will introduce another recent study on the representative elementary volume (REV) for diffusive radionuclide transport in heterogeneous clay rocks4. In this study, we present a comprehensive analysis of the heterogeneities of porosity and effective diffusivity in clay rocks by using the classical sampling theory and pore-scale simulations. First, in this study, the two-dimensional representative elementary area (REA) is correlated with the REV for porosity via a characteristic length. Next, it is shown that the REV for diffusivity is larger than the REV for porosity. Moreover, these two REVs can be correlated using Archie’s law. In such a way, the REV for diffusivity can be determined by the developed correlations through analyzing two-dimensional microstructures, thus significantly reducing the computational cost. Finally, the applicability of our approach for clay rocks is validated by experimental data on the diffusion of tritiated water in the heterogeneous SF-OPA. This study provides critical insights into the diffusion in heterogeneous clay rocks towards an enhanced predictability of radionuclide migration.
References
Bollermann T, Yuan T, Kulenkampff J, Stumpf T, Fischer C (2022) Pore network and flow field analysis towards improved predictability of diffusive transport in argillaceous host rocks. Chemical Geology 606. doi:10.1016/j.chemgeo.2022.120997
Yuan T, Fischer C (2021) Effective diffusivity prediction of radionuclides in clay formations using an integrated upscaling workflow. Transport in Porous Media 138 (2):245-264. doi:10.1007/s11242-021-01596-0
Yuan T, Fischer C (2022) The influence of sedimentary and diagenetic heterogeneity on the radionuclide diffusion in the sandy facies of the Opalinus Clay at the core scale. Applied Geochemistry (In Review)
Yuan T, Yang Y, Ait-Mouheb N, Deissmann G, Fischer C, Stumpf T, Bosbach D (2022) A comparative study on heterogeneity of clay rocks using pore-scale diffusion simulations and experiments. Journal of Geophysical Research: Solid Earth (In Review) Preprint: https://doi.org/10.1002/essoar.10511125.1
In this talk, I will first introduce our recent study on a cross-scale approach to reconstruct the pore network geometries of the sandy facies of the Opalinus Clay (SF-OPA) rock1. The resulting generalized pore network geometries are applied in digital rock models to calculate effective diffusivities, using a combined upscaling workflow for transport simulations from nanometer to micrometer scales2. We further validate the simulation results via the Positron emission tomography (PET) diffusion experiments. Next, as a follow-up study, we investigate the influence of sedimentary and diagenetic heterogeneity on heterogeneous diffusion in SF-OPA from lamina scale to drill core scale3. Our numerical results based on the simplified structural model show fast diffusion fronts in clay laminae and slow diffusion fronts in carbonate lenses and sand laminae, demonstrating the endmembers of heterogeneous diffusion patterns in SF-OPA. The sensitivity studies show that the diffusion length and homogenization time increase by up to 190% when the length and thickness of the carbonate lenses are doubled. This study provides quantitative constraints on the temporal and spatial evolution of heterogeneous diffusion at the core scale.
At last, I will introduce another recent study on the representative elementary volume (REV) for diffusive radionuclide transport in heterogeneous clay rocks4. In this study, we present a comprehensive analysis of the heterogeneities of porosity and effective diffusivity in clay rocks by using the classical sampling theory and pore-scale simulations. First, in this study, the two-dimensional representative elementary area (REA) is correlated with the REV for porosity via a characteristic length. Next, it is shown that the REV for diffusivity is larger than the REV for porosity. Moreover, these two REVs can be correlated using Archie’s law. In such a way, the REV for diffusivity can be determined by the developed correlations through analyzing two-dimensional microstructures, thus significantly reducing the computational cost. Finally, the applicability of our approach for clay rocks is validated by experimental data on the diffusion of tritiated water in the heterogeneous SF-OPA. This study provides critical insights into the diffusion in heterogeneous clay rocks towards an enhanced predictability of radionuclide migration.
References
Bollermann T, Yuan T, Kulenkampff J, Stumpf T, Fischer C (2022) Pore network and flow field analysis towards improved predictability of diffusive transport in argillaceous host rocks. Chemical Geology 606. doi:10.1016/j.chemgeo.2022.120997
Yuan T, Fischer C (2021) Effective diffusivity prediction of radionuclides in clay formations using an integrated upscaling workflow. Transport in Porous Media 138 (2):245-264. doi:10.1007/s11242-021-01596-0
Yuan T, Fischer C (2022) The influence of sedimentary and diagenetic heterogeneity on the radionuclide diffusion in the sandy facies of the Opalinus Clay at the core scale. Applied Geochemistry (In Review)
Yuan T, Yang Y, Ait-Mouheb N, Deissmann G, Fischer C, Stumpf T, Bosbach D (2022) A comparative study on heterogeneity of clay rocks using pore-scale diffusion simulations and experiments. Journal of Geophysical Research: Solid Earth (In Review) Preprint: https://doi.org/10.1002/essoar.10511125.1