Influence of small-scale heterogeneity on upward CO2 plume migration in storage aquifers |
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| Institution: | 1. School of Civil and Environmental Engineering, University of Science and Technology Beijing, 30 Xueyuan Road, Haidian District, Beijing 100083, China;2. Key Laboratory of Educational Ministry for High Efficient Mining and Safety in Metal Mine, University of Science and Technology Beijing, Beijing 100083, China;1. Department of Geosciences, National Taiwan University, Taipei, Taiwan;2. Department of Energy Resources Engineering, Stanford University, Stanford, CA, USA;1. Department of Petroleum and Geosystems Engineering, The University of Texas at Austin, TX, 78712, USA;2. Current address: Department of Chemical and Petroleum Engineering, University of Calgary, Calgary, AB, T2N 1N4, Canada;1. Uppsala University, Department of Earth Sciences, Villavagen 16, S-75236 Uppsala, Sweden;2. Lawrence Berkeley National Laboratory, University of California, Energy Geosciences Division, 1 Cyclotron Road, Berkeley, CA 94720-8126, USA |
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| Abstract: | Recent advancements in experimental techniques allow sub-core-scale heterogeneities to be quantified in a high resolution. Based on the observations of heterogeneity distributions in natural core samples, we perform simulations to study the influence of small-scale heterogeneities on large-scale CO2 migration during geological storage. We observe that even the heterogeneities at millimeter scale (the scale of a Representative Elementary Volume for sandstones) can affect large-scale buoyancy-driven upward CO2 migration. For the representative examples we study, ignoring small-scale heterogeneities can lead to an overestimation of the migration speed by a factor of two.To analyze the cause of such overestimation, we introduce a dimensionless heterogeneity factor to characterize different levels of heterogeneity. The influence on CO2 migration is quantified with respect to a variety of heterogeneity factors, correlation lengths, and fluid viscosity ratios for isotropic and anisotropic media. Our findings suggest that small-scale heterogeneities should not be ignored in core analysis, even for cores that appear relatively homogeneous and do not have distinguishable heterogeneous patterns. In addition, relative-permeability curves measured from core-flood experiments under high-flow-velocity conditions (a common practice to eliminate capillary end-effects) should not be directly used in modeling low-velocity CO2 migration if small-scale heterogeneities are present. |
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