Modeling Flow in Porous Media with Vugular Meso-scale Heterogeneities

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Arbogast0074310 Sedimentary rocks sometimes contain void regions called vugs that are much larger than the usual intergranular pores. Vugular heterogeneities raise both practical and theoretical problems for understanding fluid flow through such rocks at the field scale. For example, standard sampling methods are at a scale too small to resolve these heterogeneities. Moreover it is nontrivial to identify the correct physical formalism for modeling flow or interpreting flow measurements, and it is not clear that traditional homogenization approaches are applicable. In this project, the investigators tie microscopic (CT scan) and macroscopic measurements of a large sample (about 17,000 cubic cm) of Cretaceous carbonate rock containing centimeter-scale vugs directly to high-resolution computation of flow fields. This framework allows the testing of different physical models for flow in the geometry of the sample. The specific objectives are to: (1) Map CT scan pixels of the sample to permeability and porosity; (2) Simulate flow in the micro-scale system; (3) Determine the macro-scale governing relations for single phase flow; and (4) Determine the macroscopic model parameters in terms of the microscale characterization. Research in algorithms and upscaling procedures is conducted to achieve the second and third objectives. Subsequent numerical experiments determine the influence of alternative depositional environments and diagenetic histories by changing the connectivity of the vugs and the permeability distribution of the matrix material. This results finally in the ability to more confidently predict flow in vugular media in full-field simulations. The flow of fluids through porous rock is of economic and environmental interest. Examples include oil and gas production, obtaining adequate water supplies (groundwater accounts for about one third of the water used in the US, with many cities depending exclusively on wells), and remediating subsurface contamination at Superfund sites and many Department of Energy facilities. The sedimentary rocks through which these flows occur sometimes contain relatively large holes or void regions called vugs. The dissolution of fossil fragments is a common mechanism for creating vugs in carbonate rocks, which contain more than half the world's oil reserves and comprise many of the biggest aquifers in the US. Vugs are more conducive to fluid flow than the much smaller pore space between the rock grains, and this raises both both practical and theoretical problems for understanding large-scale flows. This project aims to construct models for this type of rock that predict the effective flow properties over hundreds of yards to several miles. Because direct experimentation over these distances is not feasible, an essential component of the research is the integration of intermediate-scale physical and large-scale computational experiments. This effort also relies on basic research in numerical algorithms and modeling techniques. Establishing the correct relations governing the flow of fluids in such rocks enables more confident predictions from full-field simulations.