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Fluid Flow, Pore Pressure, Wettability and Leakage in Mudstone Cap Rocks

Lookup NU author(s): Professor Andrew Aplin, Professor Stephen Larter


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This paper considers some of the issues surrounding the modelling of one and two phase fluid flow in mudstones. For single phase flow, key relationships include those between porosity and (a) effective stress, (b) permeability and (c) capillary breakthrough pressure. All three relationships are strongly influenced by the grain size distribution or clay fraction of mudstones, but a quantitative description is currently only available for the porosity – effective stress relationship. The importance of lithology or clay fraction as a control on the key flow properties of mudstones indicates the practical significance of estimating clay fraction directly from geophysical logs. We illustrate how Artificial Neural Networks can be used to perform this task. Having considered some of the basic flow properties of mudstones, the second part of the paper discusses aspects of two phase flow through mudstone pore systems. Rates, mechanisms and pathways of petroleum leakage through mudstone pore systems remain poorly constrained. We combine field and experimental data with theoretical arguments to suggest that once a water-wet caprock is breached, the leak path will become more oil-wet as a result of sorption of hydrophilic and ultimately hydrophobic organic compounds onto mineral surfaces. Oil-water partition of hydrophilic organic compounds in reservoirs, followed by diffusion into caprock pores may even create oil-wet pathways into caprocks and permit leakage. In these cases, caprocks simply retard the vertical migration of petroleum and column height is a function of the rates of petroleum supply and loss. Modelling the rate of loss of petroleum requires a better understanding of mudstone relative permeability.

Publication metadata

Author(s): Aplin AC, Larter SR

Editor(s): Boult P; Kaldi J

Publication type: Book Chapter

Publication status: Published

Book Title: Evaluating Fault and Cap Rock Seals

Year: 2005

Volume: 2

Pages: 1-12

Series Title: American Association of Petroleum Geologists Hedberg Series

Publisher: American Association of Petroleum Geologists

Place Published: Tulsa, Oklahoma

Library holdings: Search Newcastle University Library for this item

ISBN: 0891819010