Geochemistry of Oils in the Northern Viking Graben
The compositions of crude oils in the northern Viking graben area reflect the influence of both the types 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 on the basis of chemical composition, but with recognition of constraints on origins imposed by geographic and stratigraphic locations. Five groups are recognized: (1) Snorre oils, (2) Statfjord-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 compositions of oils in the first three groups reflect the large relative proportions of marine organic matter and the lower temperatures of expulsion characteristic of oils derived from the Draupne Formation. The compositions of oils in the last two groups reflect source rocks having more terrestrial organic matter and higher temperatures of expulsion.
The initial phase of hydrocarbon expulsion and migration from the Draupne Formation in the northern Viking graben began about 56 m.y.a. in the Troll kitchen and about 45 m.y.a. in the Oseberg kitchen. With continued subsidence and heating of Jurassic source rocks, gases and condensates were expelled, beginning about 40 m.y.a. in the Troll kitchen and about 30 m.y.a. in the Oseberg kitchen. This secondary phase of hydrocarbon generation has mixed with and displaced some of the earlier accumulations.
Figures & Tables
The success of Memoir 14 and the worldwide interest shown for data on giant fields prompted AAPG to schedule a symposium on giant fields at the end of each subsequent decade. The 1968-78 symposium was held in Houston, Texas, April 1-4, 1979, and the papers were published in AAPG Memoir 30, December 1980.
The Stavanger Conference "Giant Oil and Gas Fields of the Decade: 1978-1988" was held in Stavanger, Norway, September 9-12, 1990, and is a continuation of the Giants of the Decade series.
Scientific studies and projections of future world energy demand indicate that although alternative-energy fuel sources must be actively pursued and developed, there also must be adequate petroleum supplies to bridge the gap. For the international petroleum industry, the years covered by this conference, 1978-88, were complex. They were years of boom and bust. The world's energy consciousness was boosted sharply by the effects of the 1979 Iranian revolution and the resulting embargo, which sent world oil prices to record heights. Global petroleum exploration soon surged, leading to the industry's all-time drilling high in 1981. Then came the oil price collapse in 1985, and the following years were characterized by falling oil prices and drastic budget cuts for exploration and development.
Although exploration dropped sharply during the latter part of the decade, there was a steady flow of giant oil and gas field discoveries. Using the giant field designation criteria of 500 million bbl of oil recoverable for fields in Asiatic Russia, North Africa, and the Middle East,