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Geochemical Analyses of Oil Samples Collected in the Cantarell Oil Field, Gulf of Mexico

Jose Roberto Cerqueira1, Enrico Campos Pedroso2, Carlos Henrique Beisl2, and Fernando Pellon de Miranda1
1 PETROBRAS, Rio de Janeiro, Brazil
2 Radarsat Resource Centre in Brazil, Rio de Janeiro, Brazil

Natural oil and gas seeps have historically provided invaluable information to oil explorers in frontier areas and are evident in most offshore hydrocarbon provinces. Seepage activity indicates the presence of active petroleum systems without which there can be no accumulations.

The purpose of this study is to correlate the results of geochemical analyses of surface and subsurface oil samples in order to identify the origin of the Cantarell seep. Oil samples from a simulated spill were also analyzed as an attempt to differentiate them from seepage slicks. Analytical procedures included gas and liquid chromatography, stable isotopic composition and biomarkers techniques. Geochemical parameters that indicate source rock and thermal maturity were submitted to statistical analysis aiming at defining clusters of genetically related samples.

Petroleum in the Campeche Bay has been generated by Tithonian source rocks. In spite of the source rock common nature, subtle differences in the geochemical parameters can be observed in oils produced by different rigs from selected reservoirs. These differences are due to organic facies variability, thermal evolution and migration.

A good correlation was observed between geochemical characteristics of the seeped oil at Cantarell and the petroleum sample collected at the AKAL-G rig from the Paleocene-Cretaceous Breccia. Conversely, the petroleum spilled in the sea didn't correlate neither with the oil seep nor with the petroleum samples from the rigs.