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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 CO 2 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 CO 2 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 CO 2 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 CO 2 migration if small-scale heterogeneities are present. [ABSTRACT FROM AUTHOR]

• A new macroscopic capillary number for horizontally layered systems is presented. • Effective flow-rate dependent saturation functions are derived analytically. • A model is presented to predict the impact of laminations on CO 2 plume migration. We investigate the impact of sub-grid scale horizontal lamination on the migration of the CO 2 plume during geologic sequestration. A new physics-based model that includes the effects of capillary and viscous forces is used to obtain effective flow-rate dependent capillary pressure and relative permeability functions. For this purpose a macroscopic capillary number is derived that accurately describes the viscous-capillary force balance. The model is based on the fractional flow approach and is implemented in an extended radial Buckley-Leverett solution. This provides an easy way to investigate the impact of mm to m scale laminae on the frontal advance of the plume. Our work shows that at injection rates and volumes commonly used at geologic sequestration sites, capillary number dependency is important during the initial phase of the injection period. At later stages, the use of a capillary limit solution will be a valid approximation, even close to the injection well. [ABSTRACT FROM AUTHOR]

New guidelines and suggestions for taking reliable effective relative permeability measurements in heterogeneous rocks are presented. The results are based on a combination of high resolution of 3D core-flooding simulations and semi-analytical solutions for the heterogeneous cores. Synthetic "data sets" are generated using TOUGH2 and are subsequently used to calculate effective relative permeability curves. A comparison between the input relative permeability curves and "calculated" relative permeability is used to assess the accuracy of the "measured" values. The results show that, for a capillary number (Ncv = kLpc*A/H2μCO2qt) smaller than a critical value, flows are viscous dominated. Under these conditions, saturation depends only on the fractional flow as well as capillary heterogeneity, and is independent of flow rate, gravity, permeability, core length, and interfacial tension. Accurate whole-core effective relative permeability measurements can be obtained regardless of the orientation of the core and for a high degree of heterogeneity under a range of relevant and practical conditions. Importantly, the transition from the viscous to gravity/capillary dominated flow regimes occurs at much higher flow rates for heterogeneous rocks. For the capillary numbers larger than the critical value, saturation gradients develop along the length of the core and accurate relative permeability measurements are not obtained using traditional steady-state methods. However, if capillary pressure measurements at the end of the core are available or can be estimated from independently measured capillary pressure curves and the measured saturation at the inlet and outlet of the core, accurate effective relative permeability measurements can be obtained even when there is a small saturation gradient across the core. [ABSTRACT FROM AUTHOR]