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AAPG Bulletin


AAPG Bulletin, V. 87, No. 3 (March 2003), P. 493-506.

Copyright 2003. The American Association of Petroleum Geologists. All rights reserved.

Impact of glacially induced stress changes on fault-seal integrity offshore Norway

Balz Grollimund,1 Mark D. Zoback2

1Geomechanics International, 250 Cambridge Avenue, Suite 103, Palo Alto, California 94306
2Department of Geophysics, Stanford University, Stanford, California 94305


Balz Grollimund is working as a geomechanical consultant for Geomechanics International. He received a diploma (equivalent to M.S. degree) in structural geology from ETH in Zurich, Switzerland in 1996 and his M.S. degree and Ph.D. in geophysics from Stanford University in 1999 and 2000, respectively. During his Ph.D. in the stress and crustal mechanics group of Mark Zoback, he was studying the in-situ state of stress offshore Norway and its implications for fault-seal integrity.

Mark Zoback is professor of geophysics in the School of Earth Sciences at Stanford University. He received his B.S. degree in geophysics from the University of Arizona in 1969 and his M.S. degree and Ph.D. from Stanford in 1973 and 1975, respectively. From 1975 to 1984, he worked at the U.S. Geological Survey in the Office of Earthquake Studies. His principal scientific interests are related to the state of stress in the Earth's crust and the mechanics of crustal faulting.


We thank Norsk Hydro for generously providing the data and financial support for this study and David Wiprut for very helpful information on current leakage in the Visund, Field 3, and Field 1. We also thank Russell Davies, Scott Young, and Donald Medwedeff for their constructive reviews of the manuscript.


In this study, we use a three-dimensional numerical model of glacially related lithospheric flexure to estimate in-situ stress and pore pressure changes through time in the Norwegian sector of the northern North Sea. The model results match available borehole measurements of in-situ stress and pore pressure, which show a transition from high horizontal stresses at large distances from the coast to lower horizontal stresses in near-coastal areas and an associated rotation in stress orientation. In addition to the present-day predictions, the model results provide an estimate for the evolution of stress and pore pressure during glacial and interglacial periods. We found that the temporally changing stress field might have induced repeated reactivation of reservoir-bounding faults during the course of the Pleistocene glaciations, especially during Weichselian interglacials. As a result, hydrocarbon fields in the Norwegian offshore areas appear to have been exposed to multiple periods of fault reactivation and potential hydrocarbon leakage.

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