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Nature and causes of overpressuring in mudrocks of the Gullfaks Area, North Sea

Published online by Cambridge University Press:  09 July 2018

L. Wensaas ,
H. F. Shaw ,
K. Gibbons ,
P. Aagaard  and
H. Dypvik
L. Wensaas
Affiliation:
Dept. of Geology, University of Oslo, PO Box 1047, Blindern, 0316 Oslo 3, Norway
H. F. Shaw
Affiliation:
Dept. of Geology, Imperial College, Prince Consort Road, London SW7 2BP, UK
K. Gibbons
Affiliation:
Statoil, PO Box 300, N-4001 Stavanger, Norway
P. Aagaard
Affiliation:
Dept. of Geology, University of Oslo, PO Box 1047, Blindern, 0316 Oslo 3, Norway
H. Dypvik
Affiliation:
Dept. of Geology, University of Oslo, PO Box 1047, Blindern, 0316 Oslo 3, Norway
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Abstract

Pore-fluid pressure gradients in Lower Tertiary to Upper Jurassic mudrocks in the Gullfaks area show significant variations, both between and within individual structural compartments. Detection and quantification of abnormal pore-pressures, based on drilling parameters and wire line logs, are significantly influenced by petrological variations in the mudrocks and do not provide adequate direct pressure indicators. Empirical models show that the degree of overpressuring in mudrocks above the Gullfaks reservoirs cannot be fully explained by processes such as shale dehydration, compaction disequilibrium, aquathermal effects or in situ hydrocarbon generation, and other processes, such as caprock failure and subsequent migration of hydrocarbons (mainly gas) into the overlying mudrocks, appear to be influential in generating the observed pattern of overpressure.

Type
Research Article
Information
Clay Minerals , Volume 29 , Issue 4 , October 1994 , pp. 439 - 449
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 1994

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