SUBSIDENCE, MATURATION AND MIGRATION HISTORY OF THE TAMPEN SPUR AREA

A complete study of the petroleum system of the Tampen Spur area has b een carried out. The approach used was a two-dimensional TEMISPACK ana lysis of a seismic line crossing the area where various hypotheses cou ld be tested and later applied in a three-dimensional sense. The profi le crosses from the deepest part of the 'Tampen Graben' across the Vis und Ridge and the Marflo Ridge to the Sogn Graben in the east. Four so urce rocks have been taken into account, two marine [the Draupne (the most prolific) and the Heather] and two deltaic [the Brent and the Dun lin]. Two different prospect types can be defined: the Brent at the to p of the tilted blocks and Heather sand bodies at the foot of the erod ed tilted blocks. Various hypotheses about the geometry of these sand bodies and about the contact between the rich Draupne source rocks and the sands have been tested. Maturation started in the middle Cretaceo us, between 100 Ma in the deepest eastern part of the section (Sogn Gr aben) and 80 Ma for the Draupne on the Tampen Spur west graben. At thi s time, the structures were already sealed by the Cretaceous shales. A part from the Visund Ridge, all the prospects are currently in the con densate or gas window. Overpressures are compatible with large closed faults. More data are required about the possible sealing of minor fau lts before any conclusions can be drawn. There is no easy migration pa th from the rich Draupne rocks to the Brent reservoir and various hypo theses are discussed to explain the regional petroleum potential. One possible explanation for the regional charge is the contribution of th e other source rocks, the Heather, the Brent and the Dunlin.