oa Migration and Alteration Processes in Barents Sea Oils and Condensates - A Geochemical Appraoch

Petroleum systems in the Barents Sea were affected by repeated uplift and erosion processes which had impact on the distribution, alteration and composition of petroleums as well as on cap-rock properties. An important hydrocarbon fraction when evaluating post-emplacement alteration processes such as biodegradation, evaporative fractionation and long-distance migration are light hydrocarbons (LHC), since they make up a significant volume of oils/condensates. This study sheds light on oil-oil and oil-condensate relationships from the Hammerfest Basin and Loppa High. Analyzed condensates are altered by evaporative fractionation but do not show signs of biodegradation. Medium to high toluene contents indicate locally derived LHC with short migration distance. However, analyzed oils show clear indication of biodegradation and some being also altered by evaporative fractionation. Low content of water-soluble aromatic HC imply long-distance migrated LHC. Medium to high gas to oil ratios (GOR) for central basin samples indicate tight sealing cap-rocks, whereas samples with low GOR occur at the northern and southern tectonized basin margins, suggesting leaking cap-rocks. Tight cap-rocks might play a crucial role in the distribution as they hold back gas/condensates and favor the remigration of liquid petroleums, whereas leaking cap-rocks hold back oil and allow the gas/condensate to leak.