Source and Migration of Oil Reservoired in the Wilcox Group of the Southeast Texas Gulf Coast



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The source and maturity of hydrocarbons reservoired in the Paleocene Wilcox of the Texas Gulf Coast basin were inferred by using geochemical characteristics of the Wilcox oils in this study. Ten oil samples from eight fields collected across a 200 kilometer transect parallel to strike from depths of 7,400-11,200 feet were analyzed using high-resolution whole-oil gas chromatography (GC). Then, separation of the saturates, aromatics, resins, and asphaltenes (SARA) fractions by high performance liquid chromatography (HPLC) followed by separation of the saturates into normal paraffins, iso-paraffins, and naphthenes (PIN). The saturate and aromatic fractions were submitted for gas chromatography-mass spectrometry (GC-MS) for biomarker inversion analysis. A basin model was constructed using temperature and stratigraphic data in PetroMod2012 to numerically simulate the potential source rocks geological history and the maturation history of the Wilcox oils in this study. From the whole-oil gas chromatography and biomarker analyses, the Wilcox oils in this study are suggested to possibly be sourced from a marl-dominated rock deposited in a suboxic/oxic, low salinity, marginal marine environment with terrigenous and marine organic-matter input. The Wilcox oils in this study are inferred to have been generated in the main oil generation window with a vitrinite reflectance range of 0.6% to 0.8% at an expulsion temperature of 123℃ to 129℃. The oils are likely sourced from the Lower Wilcox or deeper formations, which entered the oil window from 40 Ma to 34.5 Ma. The whole-oil gas chromatography and biomarker analyses suggest the Wilcox oils in this study possibly share the same genetic family as the Wilcox oils from the Raccoon Bend field and the Eocene-Oligocene oils from the Blue Ridge, Brazoria, and South Liberty fields. Two Wilcox samples in this study show evidence of entrainment from lignite beds, which gives the appearance that the oils are sourced from non-marine terrigenous organic-matter input.



Wilcox, Source