--> ABSTRACT: Application of Light Hydrocarbon (C<SUB>7</SUB>) Analysis to Oil Migration and Generation in the Paradox Basin, by John R. Castano, Wallace G. Dow, Gene M. Stevenson; #91020 (1995).

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Application of Light Hydrocarbon (C7) Analysis to Oil Migration and Generation in the Paradox Basin

John R. Castano, Wallace G. Dow, Gene M. Stevenson

Analysis of C7 hydrocarbons by high resolution chromatography provides valuable data on oil genesis, alteration, maturity, and oil correlation. Paradox Basin oils are derived from Pennsylvanian Cane Creek and Paradox source rocks. Hydrocarbons in the basin are predominantly reservoired in carbonate rocks in lenticular stratigraphic traps within or adjacent to their source rocks. Therefore, very short migration prevails and the pooled hydrocarbons are closely tied to the maturity of the source beds. Seals are dense carbonates or anhydrite. Although the black organic-rich shales contain mainly type II oil generating kerogen, reliable maturity analysis was carried out by vitrinite reflectance and TAI. Most oil fields occur between VR 1.0 to 1.5%; 50° API oils occur near the 1.5% isoreflectance line. Gas production prevails at higher maturities, while only minor oil production is found between VR 0.8-1.0%. Oil correlations using the C7 data group the samples into distinct homologous sets corresponding to their host reservoirs: Paradox, Cane Creek, Mississippian and Devonian. These correlations largely coincide with those made with whole oil chromatography. Because of the high API gravity of the oils and condensates, biomarker analysis was not usable in many cases. The C7 maturity parameter, It, was used as a measure of expulsion temperature, It being independent of source rock type. In many cases oils occur reservoirs of higher paleotemperatures or maturity than the expulsion temperature showing that the oils are thermally stable up to at least VR 1.5%.

AAPG Search and Discovery Article #91020©1995 AAPG Annual Convention, Houston, Texas, May 5-8, 1995