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Abstract

(Begin page 861)

AAPG Bulletin, V. 85, No. 5 (May 2001), P. 0861-0884.

Copyright ©2001. The American Association of Petroleum Geologists. All rights reserved.

Source rock quality and hydrocarbon migration pathways within the greater Utsira High area, Viking Graben, Norwegian North Sea

Gary H. Isaksen,1 K. Haakan I. Ledje2

1ExxonMobil Upstream Research Company, 3120 Buffalo Speedway, Houston, Texas, 77252; email: [email protected]
2Esso Norge AS, N-4033 Forus, Norway; email: [email protected]

AUTHORS

Gary H. Isaksen is research supervisor for petroleum geochemistry and source rock modeling with ExxonMobil Upstream Research Company. Isaksen graduated from the University of Bergen, Norway, with an M.S. degree and a Ph.D. in petroleum geochemistry and petroleum geology. Since joining Exxon in 1985, the major themes of his work have been integration of geology and organic geochemistry, molecular geochemistry research, risking of play elements, and seep and production geochemistry. During 1993-1995 he worked established and frontier plays within United Kingdom and Norwegian territories, and during 1997-1999 he worked on regional- and prospect-scale oil and gas assessments within Azerbaijan, Turkmenistan, Uzbekistan, Kazakhstan, and Russia, as well as production geochemistry within fields of the South Caspian basin. His current geoscience focus is on applied research and the transfer of geochemical technologies within ExxonMobil's exploration, development, and production functions.

Haakan Ledje is a senior geologist with Esso Norge in Stavanger, Norway. He received his B.Sc. degree in sedimentology in 1983 from the University of Lund, Sweden, and M.Sc. degree in sedimentology and tectonics in 1985 from the University of California, Los Angeles. He also received an MBA degree in 1993 from the Norwegian School of Management, Oslo, Norway. He has broad experience with hydrocarbon systems studies on the Norwegian Continental Shelf. During 1998-1999 he was the project leader for ExxonMobil's play and prospect evaluation offshore mid-Norway. Ledje has special expertise in source rock quality assessment and hydrocarbon migration analyses.

ACKNOWLEDGMENTS

This article is published by permission of Esso Norge a.s. and Enterprise Oil Norwegian a.s. We also wish to acknowledge Robertson Research International Ltd., GeoLab Nor a.s., Saga Petroleum a.s., and Conoco Norway Inc. for permission to use some of their geochemical data in this article.

ABSTRACT

The greater Utsira High area is located within the southern part of quadrants 24 and 25 and the northern part of quadrants 15 and 16 in the Norwegian North Sea. In this part of the Viking Graben the main exploration play is the submarine fan sands of Paleocene and Eocene age. These sands (Balder, Heimdal, and Ty formations) pinch out to the east in blocks 25/8 (Jotun field) and 25/11 (Balder and Grane fields) and along the western margin of the Utsira High to form a combination of stratigraphic and structural traps. Marine sands of Middle and Late Jurassic age, typically present in rotated fault blocks, constitute another important play.

Geochemical analyses show that the Upper Jurassic Draupne Formation has a good potential for oil generation along the entire western margin and northern nose of the Utsira High. Both upper and lower Draupne source intervals along the western graben margin, however, contain more terrigenous kerogen than in the eastern part of the graben. Such change in organic facies within the Draupne source interval naturally results in a higher proportion of gas generation and the possibility for generating a more waxy crude than typically encountered in the Viking Graben. Detection and characterization of oil and gas shows within the Tertiary section permit mapping of migration entry points from the Jurassic source rocks and help delineate secondary and tertiary migration pathways within the Paleocene-Eocene play.

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