Burial, Thermal and Maturation History in the Northern Viking Graben (North Sea)

Schlakker, Attila ¹; Csizmeg, János ¹; Pogácsás, György ¹; Horti, Anikó ²
(1)Department of Physical and Applied Geology, ELTE, Budapest, Hungary. (2) MOL Oil & Gas Co., Budapest, Hungary.

In this research study burial, thermal and maturation reconstruction have been carried out using seismic and exploration wellbore data from the northern part of the Viking Graben. The study area can be found eastward from the Statfjord field in the 35/8 section.

The best source rocks located in the northern part of the Viking Graben subsided in the late Jurassic. These source rocks represented by the Kimmeridge Shale (also called Drauphne Shale) and the Heather Shale Formations of the Viking Formation Group can be found in the depth of 3000-3500 m underlain by the delta-plain deposits of the middle Jurassic Brent Group, which also have a moderate petroleum generation potential in this area. The deposition of the above-mentioned source rocks and the reservoir rocks of the northern Viking Graben are connected with the extensional event of the Pangea supercontinent in the late Jurassic - early Cretaceous. The Triassic terrestrial, alluvial and lithoral sandstones of the Statfjord Group and the middle Jurassic river bed, shoreface and delta-bar developments of the Brent Group are the primary reservoir rocks in this area. The main seal rocks of the Viking Graben are the Jurassic shales and the Cretaceous pelites.

The Jurassic organic-rich source rocks have generated hydrocarbons since the late Cretaceous. The recent thermal maturity measurements (Rock Eval analysis, vitrinite reflection measurement) on the samples from the exploration wells provided good verifying information during the modeling of the history of the thermal maturation of the source rocks and the generation of the hydrocarbons.

The source rocks of the Kimmerdige Shale, Heather Shale Formations and the Brent Group containing predominantly type II and type III kerogene have generated mainly gas in the modelling. These source rocks became mature in the late Cretaceous and have generated hydrocarbons since then, and are having petroleum generation potential nowdays, too. The gas generally migrated upward and sidelong. The migrating gas has reached the base of the Oligocene sandstones. Gas accumulates in stratigraphic traps in the Brent Group sandstones and in the Eocene sandstones.

This research couldn’t have been carried out without the help of the AAPG, and the application of the PetroMod petroleum systems modeling software supported by the IES Integrated Exploration Service, a Schlumberger Company via the PetroMod university grant program.

AAPG Search and Discovery Article #90135©2011 AAPG International Conference and Exhibition, Milan, Italy, 23-26 October 2011.