--> ABSTRACT: Thermal Modeling Using Biomarkers in the Santa Maria Basin, California, by J. David King, Paul G. Lillis; #91003 (1990).

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ABSTRACT: Thermal Modeling Using Biomarkers in the Santa Maria Basin, California

J. David King, Paul G. Lillis

During burial heating, biomarkers are altered in specific ways directly related to thermal stress; thus, they can be used as thermal maturity indicators in a fashion similar to vitrinite reflectance and Rock-Eval Tmax. Furthermore, kinetic modeling of biomarker transformations can be used to constrain interpretations of the thermal history of a rock column and thereby determine the timing and extent of other processes such as petroleum generation and mineral diagenesis.

Bitumens extracted from cuttings and core samplings of the Sisquoc, Monterey, and Point Sal formations in the Santa Maria basin were analyzed by gas chromatography-mass spectrometry for specific biomarker compounds. The results of these analyses were used to determine the thermal history at various well locations within the basin.

Geohistory diagrams were constructed from stratigraphic data (thickness, lithology, age, and paleobathymetry) and heat flow data. Effects of compaction, thermal conductivity, silica diagenesis, and eustatic sea level changes were included in the development of these diagrams.

Thermal history scenarios derived from these postulated geohistories were used to predict downhole trends in biomarker maturity indices via a computer program that used a first-order kinetic modeling algorithm. Comparison of analytical results from the bitumens with predicted trends from the kinetic model significantly constrain the geohistory of each well to a few possibilities. Further refinement of the thermal history is accomplished by ensuring that silica phase changes match the predicted maximum paleotemperature.

Preliminary results show that the central basin (Casmalia and Orcutt areas) experienced a high heat flow history and earlier petroleum generation and silica diagenesis than the rest of the basin, possibly due to early extensional tectonics.

AAPG Search and Discovery Article #91003©1990 AAPG Annual Convention, San Francisco, California, June 3-6, 1990