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Upscaling and Optimal Coarse Grid Generation for the Numerical Simulation of Two Phase Flow in Porous Media Hassan Mahani Centre for Pet by bmd18385


									 Upscaling and Optimal Coarse Grid Generation for the

Numerical Simulation of Two-Phase Flow in Porous Media

                       Hassan Mahani

                     Centre for Petroleum Studies
            Department of Earth Science and Engineering,
           Imperial College London, London SW7 2AZ, UK

Flow in porous media is affected by properties and processes that occur on all scales
such as reservoir heterogeneity. Numerical models are often used to predict the
behavior of flow in these systems. However such models cannot represent explicitly
processes/properties on all scales and the level of details that can be incorporated in a
simulation model is constrained by the computational capacity and resources
available. “Upscaling’ of small scale properties/processes is used to transfer
information from scale of measurement(small) to a larger scale to study the physical
impact of subgrid scale properties sand process on the scale that governing equations
are explicitly expressed. Although there is an extensive literature demonstrating that
the large grid flow equations may not be the same as those on the small scale, the
most commonly applied methods assume that form of flow equations doesn’t change
with change of scale and involve the use of an effective permeability and modified
relative permeabilities often combined with specialized gridding techniques.
   Indeed careful coarse grid generation can improve performance of upscaling and
remove the requirement to upscaling multi-phase flow properties. In essence all these
methods attempt to minimize differences between fine and coarse grid simulations by
optimizing the location of coarse grid block boundaries. Permeability-based
techniques preserve the variation of permeability within the coarse grid resulting in
finer gridding around regions of extreme permeability, while flow-based techniques
refine the grid in areas of high flow-rate.
   In this thesis a novel grid coarsening technique has been developed that is based
upon conserving vorticity in the flows through heterogeneous porous media while
scale of simulation changes. We optimize location of coarse grid boundaries by firstly
recognizing areas of high and low vorticity from single-phase flow simulation. We
then generate simulation models which are more refined in the areas of high vorticity
intensity and coarser in low vorticity. We finally demonstrate the successful
application of the method to two-phase simulations in a range of heterogeneous
models. This robust technique provides an insight into the success of the existing
flow-based and permeability-based griddings and essentially incorporates both flow
effects and geology complexity in gridding.

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