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The AAPG/Datapages Combined Publications Database

AAPG Special Volumes


Pub. Id: A031 (1985)

First Page: 403

Last Page: 441

Book Title: SG 20: Alaska North Slope Oil-Rock Correlation Study: Analysis of North Slope Crude

Article/Chapter: Petroleum Geochemistry of Oil and Sediment Samples from the NPRA, Alaska: SOURCE ROCK EVALUATION INCLUDING ISOTOPES AND BIOMARKERS

Subject Group: Geochemistry, Generation, Migration

Spec. Pub. Type: Studies in Geology

Pub. Year: 1985

Author(s): P. J. D. Park, G. P. Cooles, S. W. Lister


Using inspection properties alone it was possible to divide 7 of the two groups defined by Magoon and Claypool. The Umiat No. 4 Simpson Core Test, and the Cape Simpson Area oils fall in the Simpson-Umiat group while the Put River Dalton No. 1, Fish Creek No. 1, and the South Barrow No. 19 oils fall in the Barrow-Prudhoe group. The Barrow No. 20 oil is considered to be a mixture of both eyes, whereas the Seabee No. 1 condensate is anomalous and may represent an entirely different group.

Gas chromatographic-mass spectrometry (GC-MS) and stable carbon isotope ratios of the whole oil and the oil fractions show concurrence with the above grouping but suggest there may be more of a mixing or continuum of properties than is implied by the concept of grouping.

Three of the oils,Dalton,Fish Creek, and the Cape Simpson area, have undergone varying degrees of biodegradiasd have lost their normal alkanes. The Simpson Core Test sample shows evidence of heavy biodegradation (presence of normethyl hopanes), but n-alkanes are still present. This suggests an earlier period of biodegradation followed by subsequent topping up with normal oil. A similar process is suggested to explain the composition of the Dalton oil

The majority of the sediment samples had good organic carbon contents (TOC > 1.0 wt.%) but poor hydrocarbon source potentials. This and the general high maturity suggest that oil or gas generation has already occurred in most of the sediments examined, the shallower Torok and pebble shale samples excepted. The presence of inert carbon and the humic nature of most of the samples may be partially responsible for the low potentials observed.

The very small amounts of extracted hydrocarbons recovered from the Kingak and Torok in Seabee No. 1 and the Shublik and Echooka formations in Inigok No. 1 were similar in nature and considered to be nonindigenous, probably contaminants.

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