Triassic Source Facies in High Paleo-Latitude
Petroleum
Systems
By
A. Holba (Phillips Petroleum
Co.), W.D. Masterson
(Phillips Alaska, Inc.), L. Ellis (Terra Nova Technologies), and L. Dzou (BP
Upstream Technology Group)
Oils derived from the Triassic Shublik Formation of
the North Slope of Alaska are prolific and well studied. However, the Shublik
sourced system
is not unique; other Triassic
petroleum
systems exist in high
northern latitudes. Triassic oils are found from the Chukchi Sea, across Alaska
through Canada and as far east as the Barents Sea of Norway. Age and
environmental diagnostic geochemical indicators were used to describe and
differentiate oils of the Triassic
petroleum
system
from oils from other
possible sources, particularly Jurassic derived oils worldwide. Triassic oils
have some distinct characteristics when compared to Cretaceous, Jurassic, and
Upper Paleozoic derived oils. Marine Triassic-derived oils are isotopically
negative (<-29), have high extended tricyclic terpanes, and generally possess
dinosteranes and 4-methylsteranes. They contain little or no 24- norcholestanes
(C26 steranes) or oleanane.
We report a new ratio to be a reliable source age parameter when evaluating oils and rock extracts: Extended Tricyclic Terpane Ratio (ETR) [sum of C28 and C29 tricyclic terpanes /18-a(H)- trisnorhopane (Ts)]. Both the numerator and denominator are thermal maturation and biodegradation resistant, thus minimizing these effects. This is a more robust source related age and correlation parameter, useful for a wide range of applications. Note that Triassic oils tend to have a high ETR (>2.0) and that Jurassic oils are not observed to have a high ratio.
AAPG Search and Discovery Article #90008©2002 AAPG Pacific Section/SPE Western Region Joint Conference of Geoscientists and Petroleum
Engineers, Anchorage, Alaska, May 18–23, 2002.