Precise numerical modelling of physical transport in strongly heterogeneous porous media
Published:January 01, 2005
Zhongqiang Xie, Rae Mackay, K. Andrew Cliffe, 2005. "Precise numerical modelling of physical transport in strongly heterogeneous porous media", Understanding the Micro to Macro Behaviour of Rock–Fluid Systems, R. P. Shaw
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A library comprised of precise numerical simulation results for two-dimensional flow and advective transport through statistically-equivalent, structured, porous media is being created to investigate upscaling procedures for contaminant dispersal and physical transport at large space and long time-scales. Several technical challenges were overcome to achieve high precision in the velocity fields and particle paths. A Cholesky Decomposition method for efficient media generation has been extended to generate ‘artefact’-free, areally-extensive random fields of hydraulic conductivity variation. An efficient mixed finite-element method, capable of handling periodic boundary conditions was used to compute the flow distributions through the generated media. The method permits exact solution of particle trajectories. Comparison of particle migration patterns with available analytical solutions confirms persistent non-Fickian behaviour of particle migration at large space and times-scales, as well as confirming the accuracy of the simulations. Boundary effects on particle trajectories are found to be significant and cannot be removed totally from the steady-state flow fields. Periodicity, both parallel and perpendicular to the flow direction, results in particle trajectories that are almost periodic and so are inappropriate for transport studies of realistic media. A compromise solution has been adopted whereby only the domain boundaries parallel to the flow are periodic.
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Understanding the Micro to Macro Behaviour of Rock–Fluid Systems
Understanding how fluids flow through though rocks is very important in a number of fields. Almost all of the world's oil and gas are produced from underground reservoirs. Knowledge of how they got where they are, what keeps them there and how they migrate through the rock is very important in the search for new resources, as well as for maximising the extraction of as much of the contained oil/gas as possible. Similar understanding is important for managing groundwater resources and for predicting how hazardous or radioactive waste or carbon dioxide will behave if stored or disposed of underground. Unravelling the complex behaviour of fluids as they flow through rock is difficult, but important. We cannot see through rock, so we need to predict how and where fluids flow. Understanding the type of rock, its porosity, the character and pattern of fractures within it and how fluids flows through it are important. Some contributors to this volume have been trying to understand real rocks in real situations and others have been working on computer models and laboratory simulations. Put together, these approaches have yielded very useful results, many of which are discussed in this volume.