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Biomarker analysis of the Vallecitos Syncline, San Joaquin Basin

Oil family distributions
The geochemical work for this project by graduate student Meng He comprises two components. First, biomarker and diamondoid analyses were conducted on 23 black oil samples, 2 seeps, and 1 gas condensate from the syncline. These samples were provided by the U.S. Geological Survey from their extensive collection of oils from the San Joaquin Basin. The aim of this geochemical analysis was to test the results of the basin and petroleum system model, which indicate that there are two source rocks generating petroleum in the syncline.  Early results confirm that Vallecitos oil is a mixture of two oil types. Although liquid-source rock correlation studies are lacking, we strongly suspect that the two oil types are derived from the Eocene Kreyenhagen Formation and Cretaceous Moreno Formation.
 
The second geochemical component of this study involves sending rock samples to an independent lab for Rock-eval (Tmax) and vitrinite reflectance (Ro) measurements. These measurements are essential for calibrating the 1-D and 2-D basin and petroleum system models, which currently are uncalibrated. (Describe the well) Ro measurements were made at 3 sample depths spanning feet in the Kreyenhagen Formation; all 3 points average about 0.6 Ro, indicating that that uppermost part of that formation is thermally immature or just entering the oil window in the deepest part of the syncline.  Similarly, 20 Tmax measurements spanning xx feet depth in the Kreyenhagen Formation average 420°C, indicating these rocks are thermally immature.