Calculating Effective Absolute Permeability in Sandstone/Shale Sequences

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Abstract
Summary: Two averaging algorithms are proposed for determining block effective absolute permeability. The experimental relationship between the effective permeability, the volume fraction of shale, and the anisotropy of the shales is first observed through repeated flow simulations. A power-averaging model and a percolation model are proposed to fit the experimentally observed relationship. The power-averaging model provides a surprisingly easy and efficient way to calculate block effective absolute permeability. A simple graph is given to determine the averaging power from the geometric anisotropy (aspect ratio) of the shales for both vertical and horizontal steady-state flow. The effective absolute permeability can then be calculated with the averaging power, the volume fraction of shale, and the component sandstone and shale permeabilities. The effective permeability of a sandstone/shale sequence is affected when the shales are large with respect to the size of the gridblocks. A correction for large shales relative to small gridblocks is also proposed.