40 oil samples from across the N Slope of Alaska have been analyzed by the US Bureau of Mines and the US Geological Survey. Results of these analyses suggest 2 separate genetic oil types. The first, the Simpson-Umiat oil type, occurs in reservoir rocks of Cretaceous and Quaternary age. These are higher gravity, low- sulfur oils with no, or slight, odd-numbered n-alkane predominance and pristane to phytane ratios greater than 1.5. The second type, the Barrow-Prudhoe oil type, occurs in reservoir rocks of Carboniferous to Cretaceous age. Physical properties of these oils are variable, but in general the oils are medium-gravity, high-sulfur oils with slight even-numbered n-alkane predominance and pristane to phytane ratios less than l.5. The 2 types are believed to originate from different source rocks.
Additional Publication Details
Two oil types on North slope of Alaska; implications for exploration
American Association of Petroleum Geologists Bulletin