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The AAPG/Datapages Combined Publications Database

AAPG Special Volumes


Pub. Id: A031 (1985)

First Page: 123

Last Page: 137

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

Article/Chapter: Carbon Isotopic Characterization of Some North Alaska Petroleums and Potential Source Rock Kerogen Assemblages: BASIC SOURCE ROCK EVALUATION AND CARBON ISOTOPE

Subject Group: Geochemistry, Generation, Migration

Spec. Pub. Type: Studies in Geology

Pub. Year: 1985

Author(s): R. Burwood, G. A. Cole, R. J. Drozd, H. I. Halpern, I. E. Penfield, R. A. Sedivy


A source-to-petroleum correlation between five possible source units and a group of nine oils representative of the Alaskan North Slope has been attempted. A program was pursued to examine the utility of a stable carbon isotopic comparison of source kerogen-kerogen pyrolyzates with the petroleums.

Of the sediment spot horizons studied, only the Echooka was without discernible source potential. The remaining sediments showed varying degrees of source richness. Unfortunately, half the sediments proved to be unsuitable for kerogen pyrolyzate production, being of advanced thermal maturity and partially to fully spent. This included the majority of the pre-Cretaceous examined. Using the pebble shale-Torok Formation as a datum, maturity increased rapidly to the south, in the direction, of the Colville Trough, and less rapidly east to west.

Three limiting groups of oils were recognized using isotopic and compositional information. These groups were best typified by the Put River, Simpson, and Seabee petroleums, each showing a progressive 13C enrichment. Additionally, other oils showed characteristics suggestive of mixing phenomena. The Put River oil was believed to be representative of the major economic oil type of North Alaska.

Despite large kerogen-kerogen pyrolyzate differentials, no convincing isotopic match was observed between the pebble shale or Torok formations and either the Put River or Simpson oils. Similarly, the limited Kingak Formation data showed equivocal correlations with the oils and again large-kerogen-kerogen pyrolyzate differentials. It is therefore possible that direct correlation of source and petroleum on a whole kerogen ^dgr13C basis may be fallible. All three Shublik specimens were spent; however, two showed residual kerogen carbon isotopic values consistent with possible correlation with the Prudhoe oil type.

Although the petroleums provided a good basis for correlation, it was regrettable that additional sediments of appropriate maturity and representative of regional plus stratigraphic facies variation were not available for this study.

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