A drain in my graben: an integrated study of the Heimdal area petroleum system

We report a coupled geochemical, fluid inclusion, structural and basin mode lling study of the North Sea's greater Heimdal petroleum system. The Heimda l High has acted as a major conduit for vertical petroleum migration since the early Tertiary. Petroleum generated within the Viking Graben is focused laterally along a faulted Jurassic carrier system to the Heimdal High. Ver tical migration through 1-2 km of Cretaceous mudstones to Tertiary sands oc curred at the Heimdal High under pressure regimes ranging from hydrostatic to highly overpressured. There is no need to invoke vertical migration thro ugh faults and hydrofractures, although this cannot be ruled out. Lateral m igration in the Tertiary sands takes place from the Heimdal High feed point ; oil and gas migrate laterally and (locally) vertically to reach the highe st Tertiary sand at most locations. Most migration to current accumulations is very late in the Neogene. We speculate that vertical migration within t he Tertiary may be partly controlled by small-throw polygonal fault systems in places where sand has been injected along the faults. (C) 2000 Elsevier Science B.V. All rights reserved.