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Staale Monstad1, Martin Bernard Gowers2, Tove S. Sjoblom2
(1) Norsk Hydro, Technology and Competence, Bergen, Norway
(2) Norsk Hydro Exploration, Oslo, Norway

Abstract: Facies control on hydrocarbon migration and accumulation. An integrated study from the Middle Jurassic in the Heimdal area offshore Norway

The Heimdal area is located just north of the Utsira High, offshore western Norway and includes the Middle Jurassic discoveries Frøy, Rind, Vale, Byggve and Skirne.

The Brent equivalent Vestland Group (Hugin + Sleipner formations) that constitutes the main reservoir in all the Jurassic discoveries, show a strong variation in both thickness and character over the area. It is onlapping the Utsira High to the south and reaches a thickness of more than 400 metres 30 km further north. In addition, parts of the Hugin Fm. show very rapid lateral facies shifts in this area. These rapid shifts results in corresponding seismic facies changes and reduced reflector- continuity, emphasising the need for strong integration between geophysics and geology.

The Vestland Gp. was deposited as a southern continuation of the retreated Brent delta in an overall transgressive regime. However, sedimentological analysis suggests at least one period of relative sea-level fall during the Late Bajocian-Early Bathonian in the Heimdal area. This sea-level fall led to deep incision (30m) in the Frøy area and a pronounced basinward shift in the Rind area, (seaward from Frøy). Coarse and very coarse sand were deposited on top of silty bay-fill sequences (Frøy area) and lower shoreface silty-sands (Rind area), leading to a dramatic shift in reservoir parameters across the sequence boundary. As a result of this, the sequence boundary act as a major control on the migration and accumulation of hydrocarbons into the Middle Jurassic structures in the area.

AAPG Search and Discovery Article #90914©2000 AAPG Annual Convention, New Orleans, Louisiana