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ABSTRACT: Faults, oil migration, overpressure and dismigration - dating events. A case history from the Halten Vest high pressure region, offshore Norway

Karlsen, Dag A.1, Kristian Backer-Owe1, Knut Bjørlykke1, Kari Berge2, and Rainer G. Schaefer3
(1) University of Oslo, N-0316 Oslo, Norway 
(2) Enterprise Oil Norge Ltd, N-4001 Stavanger, Norway 
(3) Institute of Petroleum and Organic Geochemistry, Forschungszentrum Jülich, D-52425 Jülich, Germany

Geochemical evidence from core extracts and fluid inclusions in diagenetic quartz overgrowths is used to shed light on overpressure development and palaeo-leakage of oil from currently dry structures in the Haltenbanken area offshore Norway. Fluorescent oil type inclusions in quartz in the Smørbukk field suggest that oil migrated into this structure already 70-40 million years ago. The same scenario applies to the currently dry structures 6506/12-4, and 6506/11-1 west of the main Smørbukk fault zone. Geochemical analysis of the oil in the petroleum inclusions in these dry structures as well as in Smørbukk provide evidences that these structures were initially filled with petroleum derived from the Spekk Formation. At this early time was there no mature source rocks at the Spekk Fm. level in the current drainage area of these dry structures nor in the drainage are of the nearby Smørbukk Sør field. It follows that at this early time oil must have entered into Smørbukk from areas to the west-south west through the currently pressure sealing fault zone which marks the westward limitation of the Smørbukk field. The process that caused this fault zone to become sealing, probably diagenesis, also caused the later overpressure development and oil loss from the 6506/12-4, and 6506/11-1 structures as overpressure built up regionally at the Lower Cretaceous datum which constitutes the cap-rock border zone. We provide evidence to suggest that regional pressure build-up must have occurred during the last 3 million years.

AAPG Search and Discovery Article #90913©2000 AAPG International Conference and Exhibition, Bali, Indonesia