Saturated and olefinic terrigenous triterpenoid hydrocarbons in a biodegraded tertiary oil of northeast Alaska

Dinorlupanes, norlupanes, olean-12-ene, 18α-olean-12-ene and urs-12-ene occur in a heavily biodegraded Tertiary oil tested from the OCS-Y-0849-1 well, drilled on the Hammerhead Prospect in the Beaufort Sea, offshore northeast Alaska. These indicators and other source-related characteristics of the Hammerhead oil (ring-A degraded oleanoids, ursanoids and lupanoids; [V] and [Ni] less than 2.0 ppm; V/(V + Ni) less than 0.5) indicate a land-plant, angiospermous character in the source facies. The olefins in the Hammerhead and Canadian oils are considered to be contributed directly from the source, rather than extracted from adjacent immature (non-source) sediments during migration, as indicated by (a) the accompanying presence in the oil of saturated angiosperm markers, and (b) the absence of measurable amounts of other olefins characteristic of immature organic matter (e.g. diasterenes and hopenes).