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A Logical Error in Gassmann Poro-Elasticity
- Publisher: European Association of Geoscientists & Engineers
- Source: Conference Proceedings, EAGE 2020 Annual Conference & Exhibition Online, Dec 2020, Volume 2020, p.1 - 5
Abstract
Summary
The well-known Gassmann equation for the fluid dependence of rock compressibility is in error, because of a mistake in its derivation, obvious once stated. The mistake is the application of an open-systems theorem to the hydraulically-closed system ( undrained ) of low-frequency wave propagation. This error (NOT solid micro-heterogeneity) is responsible for the difference between Gassmann's result and the prior result by Biot, or the subsequent, equivalent result by Brown and Korringa. Hence, we should use these instead, for interpreting 4D seismic differences. The additional parameter, a rock property, may be measured by quasi-static compression tests.
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