Geochemical investigation of the mechanisms of hydrocarbon generation and accumulation in the Uinta Basin, Utah

This study undertook an experimental investigation of the mechanisms of hydrocarbon generation and accumulation in the Uinta Basin, Utah. While the Uinta Basin and the Green River Formation historically have received considerable attention from both geologists and organic geochemists, the present study was unique in that it combined analyses of representative source rocks from the entire Tertiary stratigraphic section with detailed laboratory simulation experiments. The results of these analyses offer new insights for characterization of lacustrine source rock lithofacies, gas-oil-source rock correlations, hydrocarbon generation kinetics, and basin modeling. One of the most significant findings was that the classic Type I kerogen contained in offshore open lacustrine source rocks like the mahogany shale was not the source of waxy crude oils produced from deep overpressured reservoirs in fields such as the Altamont-Bluebell. The true source of these oils was from a distinct sulfur-rich Type I kerogen found in nearshore open lacustrine source rocks of basal black shale facies, a stratigraphic unit assigned herein to the lower Green River Formation.; In association with the comprehensive series of hydrous pyrolysis experiments performed in this investigation, a detailed examination was made of maturity variations in bulk chemical characteristics and molecular compositions of the products generated. The results of these analyses provide a greater understanding of mechanisms of petroleum generation and the interrelationships between various organic phases. In addition, variations observed in many common biomarker maturity parameters were determined to result primarily from differential rates of generation/degradation rather than from conventional product/precursor relationships.