We have developed and implemented a multiphase and multicomponent dual porosity model in a 3-D flow and transport numerical model called UTCHEM in order to evaluate the potential of current characterization and remediation technologies of nonaqueous phase liquids (NAPLs) in fractured porous media. Many natural porous media are fractured and some contain NAPL contamination. For example, the Bear Creek Burial Grounds at Oak Ridge Laboratory and the Test Area North at Idaho National Laboratory are sites with fractured media contaminated by dense NAPLs.
A dual porosity model of fractured porous media assumes that there are two distinct physical systems: the high permeability, low storage capacity fracture network and the low permeability, high storage capacity matrix. The dual porosity formulation allows flow in both matrix and fracture. The multiphase transfer flow between the fracture and matrix rock is calculated from a transfer function that is based on the Warren and Root theory. Mass transfer between the fracture and matrix rock includes diffusion, convection, imbibition, and gravity drainage. The dual porosity model adds additional subgridding to the main finite difference grid. The matrix blocks are divided into smaller sections, so that the transport within the blocks can be modeled accurately.
Several researchers have performed laboratory solute transport experiments in single-fracture columns to investigate processes such as matrix diffusion, dispersion, and adsorption. Deeds investigated the phase transfer and transport of partitioning tracers through single-fracture columns both with and without residual NAPL. The objectives of this work are:
to develop a multiphase, multicomponent dual porosity model to simulate PITTs in fractured media,
to study the impact of matrix diffusion on the transport of those tracer compounds typically used in PITTs, and
to evaluate the PITT as a technique for estimating NAPL volumes in fractured media.
Center for Petroleum and Geosystems Engineering
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The University of Texas at Austin
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