Abstract
Large-scale (cm and greater) heterogeneities raise both practical and theoretical problems for understanding fluid flow through rocks that contain them. Standard sampling methods such as thin sections, core plugs, and even whole core are at a scale too small to resolve these heterogeneities, and direct measurement of flow properties is not straightforward. Moreover it is not obvious what physical formulism (e.g., Darcy's law, Forchheimer's Law, Stokes flow) is appropriate for modeling flow or interpreting flow measurements, nor is it clear that traditional homogenization approaches (e.g., effective medium theory, renormalization, dual-porosity) are applicable in such systems. We report simple measurements on a large 25 cm diameter by 36 cm high sample of Cretaceous carbonate containing centimeter-scale vugs, and compare them to flow fields computed from high-resolution CT images of the same sample. These computations use a single-physics Darcy-flow model. We also compute passive tracer transport in the same model to evaluate preferential flow paths within the rock. The direct computations are based on a porosity grid extracted from a set of CT images (512 × 512 × 240 pixels, 0.5 mm resolution) of the large sample. We also use the single-physics model to estimate the length scale of connections between vugs in this sample. The results demonstrate the need for upscaling methods that preserve connectivity of features in highly heterogeneous rocks.
