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Abstract

AAPG Bulletin, V. 100, No. 5 (May 2016), P. 723-742.

Copyright ©2016. The American Association of Petroleum Geologists. All rights reserved.

DOI: 10.1306/02011614222

Effective flow properties of heterolithic, cross-bedded tidal sandstones: Part 2. Flow simulation

Benoît Y. G. Massart,1 Matthew D. Jackson,2 Gary J. Hampson,3 and Howard D. Johnson4

1Department of Earth Science and Engineering, Imperial College London, South Kensington Campus, Prince Consort Road, London SW7 2BP, United Kingdom; present address: Statoil ASA, Sandsliveien 90, Bergen 5254, Norway; [email protected]
2Department of Earth Science and Engineering, Imperial College London, South Kensington Campus, Prince Consort Road, London SW7 2BP, United Kingdom; [email protected]
3Department of Earth Science and Engineering, Imperial College London, South Kensington Campus, Prince Consort Road, London SW7 2BP, United Kingdom; [email protected]
4Department of Earth Science and Engineering, Imperial College London, South Kensington Campus, Prince Consort Road, London SW7 2BP, United Kingdom; [email protected]

ABSTRACT

Tidal heterolithic sandstone reservoirs are heterogeneous at the submeter scale because of the ubiquitous presence of intercalated sandstone and mudstone laminae. Core-plug permeability measurements fail to sample a representative volume of this heterogeneity. Here, we investigate the impact of mudstone drape distribution on the effective permeability of heterolithic, cross-bedded tidal sandstones using three-dimensional, surface-based “minimodels” that capture the geometry of cross beds at an appropriate scale. The impact of seven geometric parameters has been determined: (1) mudstone fraction, (2) sandstone laminae thickness, (3) mudstone drape continuity, (4) toeset dip, (5) climb angle of foreset–toeset surfaces, (6) proportion of foresets to toesets, and (7) trough or tabular geometry of the cross beds.

We begin by identifying a representative elementary volume of 1 m3 (∼35 ft3), confirming that the model volume of 9 m3 (∼318 ft3) yields representative permeability values. Effective permeability decreases as the mudstone fraction increases, and it is highly anisotropic: vertical permeability falls to approximately 0.5% of the sandstone permeability at a mudstone fraction of 25%, whereas the horizontal permeability falls to approximately 5% and approximately 50% of the sandstone value in the dip (across mudstone drapes) and strike (parallel to mudstone drapes) directions, respectively. Considerable spread exists around these values, because each parameter investigated can significantly impact effective permeability, with the impact depending upon the flow direction and mudstone fraction. The results yield improved estimates of effective permeability in heterolithic, cross-bedded sandstones, which can be used to populate reservoir-scale model grid blocks using estimates of mudstone fraction and geometrical parameters obtained from core and outcrop-analog data.

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