Porosity and pressure: Role of compaction disequilibrium in the development of geopressures in a Gulf Coast Pleistocene basin
- 1 January 1995
- journal article
- Published by Geological Society of America in Geology
Abstract
Measured pressures in Pleistocene strata of the Eugene Island block 330 area of offshoreLouisianareachapprox.nine-tenthsofthelithostaticpressuresbelow2kmdepth; three-fourths of these geopressures are due to compaction disequilibrium. We show the relation between effective stress and porosity for compacting sediments to be exponential in shallow, normally pressured strata, then use the relation to calculatefluid pressure at depthingeopressuredstrata.Measuredpressuresbelow2kmexceedourpredictedvalues. Aplotofeffectivestressvs.porositydemonstratesthatcompactiondisequilibriumaccounts for about three-quarters of the overpressures. We infer that the remainder must be due to pore-pressuregenerationatdepththatoccurredaftertherocksreachedtheirpresentporosity.Keywords
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