Abstract
This is a geochemical study of oils from seven fields (La Victoria, Guafita, Caipe, Silvestre, Sinco, Silvan and Palmita) in the Barinas sub-basin, Venezuela. The study focused on the type and quality of the crude oils, their relative correlation, degree of maturation, alteration and the depositional paleoenvironment of the source rock. The crude oils of the Barinas sub-basin can be classified in the range of paraffinic-naphthenic (La Victoria and Guafita) to aromatic-naphthenic (Caipe, Silvestre, Sinco, Silvan and Palmita). These crude oils were probably all generated from a similar source rock interval but with lateral variations in lithofacies and redox potential across the Basin. We interpret all of the crude oils to have been sourced from marine, algal and bacterial organic matter with a systematic variation in terrigenous organic content of the source rock. Bulk elemental and biomarker geochemistry indicators suggest that La Victoria and Guafita crude oils were generated from organic matter deposited in a more siliciclastic dominated lithofacies. Crude oils from the Caipe, Silvestre, Sinco, Silvan and Palmita fields seem to have been generated from a more calcareous lithofacies. Based on interpretation of thermal indicators from saturate and aromatic biomarkers all of the oils studied were generated during peak levels of maturation of the source rock. La Victoria and Guafita crude oils seem to have been generated at slightly lower thermal maturities than the other crude oils studied. The oils in some of these fields have undergone extensive biodegradation and water washing, hydrocarbon recharge and later incipient biodegradation of the recharged crude. This explains much of the chemical and physical properties variability observed across individual fields and between accumulations.
Published Version
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