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AAPG Bulletin

Abstract

Alteration Trends in Barents Sea Petroleums

AAPG Bulletin, V. 100, No. 2 (February 2016), P. 165-190.

Copyright ©2016. The American Association of Petroleum Geologists. All rights reserved.

DOI: 10.1306/08101514152

Regional petroleum alteration trends in Barents Sea oils and condensates as a clue to migration regimes and processes

Benedikt Lerch,1 Dag Arild Karlsen,2 Tesfamariam Berhane Abay,3 Deirdre Duggan,4 Reinert Seland,5 and Kristian Backer-Owe6

1Department of Geosciences, University of Oslo, P.O. Box 1047 Blindern, N-0316 Oslo, Norway; [email protected]
2Department of Geosciences, University of Oslo, P.O. Box 1047 Blindern, N-0316 Oslo, Norway; [email protected]
3Department of Geosciences, University of Oslo, P.O. Box 1047 Blindern, N-0316 Oslo, Norway; [email protected]
4Noreco, Postboks 550 Sentrum, 4003 Stavanger, Norway; [email protected]
5Noreco, Postboks 550 Sentrum, 4003 Stavanger, Norway; [email protected]
6Department of Geosciences, University of Oslo, P.O. Box 1047 Blindern, N-0316 Oslo, Norway; [email protected]

ABSTRACT

To date, most condensates and gases found in the Hammerfest Basin exist in distal, central basin settings, in traps with tight cap rocks of class 1 traps, whereas low-gas–oil-ratio (GOR) oils occur systematically in proximal basin settings, where cap rocks of class 3 traps prevail. Multiple fill-spill events resulted in the redistribution of oils toward structurally higher basin margins. In a systematic evaluation of light hydrocarbon parameters from condensates and oils, it was found that oils in general exhibit more traceable alteration effects than do condensates. Whereas 75% of condensate and 13.3% of oil samples are fractionated, 6.25% and 10%, respectively, show signs of biodegradation. Long-distance migration is indicated for 12.5% of condensate and 50% of oil samples. In addition, clear evidence is shown for the mixing of recently migrated high-GOR petroleum phases with older, low-GOR paleo oils. In general, variation in source-specific parameters is surprisingly less pronounced. Decreasing thermal maturity of entrapped petroleum from the eastern part of the Tromsø Basin toward the Måsøy-Nysleppen Fault Complex is observed, whereas high maturities are shown for the Nordkapp Basin and the Finnmark Platform in the eastern part of the study area. Low-to-medium maturities are recorded for oils from the basin margins of the Hammerfest Basin. Alterations in the composition of the petroleums by physiochemical processes and distribution patterns of the petroleums are closely associated with uplift and erosion.

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