ABSTRACT: Geochemistry of Oil in the Northern Viking Graben

H. M. Chung, W. S. Wingert, G. E. Claypool

The composition of crude oils in the northern Viking Graben area reflects the influence of both the type of organic matter and the thermal maturity of Jurassic source rocks in the major basin depocenters, referred to as the Oseberg and Troll kitchens. Forty-four oil samples were analyzed and classified primarily based on chemical composition, but with recognition of constraints on origins imposed by geographic and stratigraphic locations. Five groups are recognized: (1) Snorre oils, (2) Stratfjord-Gullfaks oils, (3) Brent-Oseberg Beta-Veslefrikk oils, (4) Oseberg Alpha-Troll oils, and (5) Agat and Blocks 35/8 and 35/11 oils. The composition of oils in the first three groups reflects the large relative proportions of marine organic matter and the lower expulsion temperatur s characteristic of oils derived from the Draupne Formation. The composition of oils in the last two groups reflects source rocks having more terrestrial organic matter and higher expulsion temperatures.

The initial phase of hydrocarbon expulsion and migration from the Draupne Formation in the northern Viking Graben began about 56 Ma in the Troll kitchen and about 45 Ma in the Oseberg kitchen. With continued subsidence and heating of Jurassic source rocks, gases and condensates were expelled beginning about 40 Ma in the Troll kitchen and about 30 Ma in the Oseberg kitchen. This secondary phase of hydrocarbon generation has mixed with and displaced some of the earlier accumulations.

AAPG Search and Discovery Article #91000©1990 AAPG Conference-Giant Oil and Gas Fields of the Decade 1978-1988 Conference, Stavanger, Norway, September 9-12, 1990