Comparison of crude oils found in carboniferous reservoir rock and potential source rocks in the Black Warrior Sasin, Southeastern United States

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University of Alabama Libraries

The Black Warrior basin in northwestern Alabama achieved maximum burial, maturation, and subsequent cessation of hydrocarbon generation during Late Permian time. The Chattanooga and Floyd/Neal Shales are viable potential source rocks for the Carboniferous sandstone reservoirs in the Black Warrior basin. To determine which source rock produced the crude oil in the Carboniferous-aged North Blowhorn Creek and Chicken Swamp Branch Oil Fields, this study uses Rock-Eval Pyrolysis and biomarker analyses. This study establishes total organic content (TOC) values ranging from 2.92 to 6.25% (4.29% average) in the Chattanooga Shale, and 0.62 to 3.16% (1.86% average) in the Floyd/Neal Shale. These values, in tandem with Rock-Eval Pyrolysis data, display previous expulsion and potential future expulsion of hydrocarbons from both potential source rocks by showing established maturation levels based on Tmax values and ample amounts of organics necessary to expel hydrocarbons. Gas Chromatography-Mass Spectrometry results show that the C27-29 sterane levels and pristane/phytane ratios are similar in the Carter sandstone crude oils, the Pottsville A sand crude oils and the Floyd/Neal Shale samples. No discernible similarities or patterns between the crude oils and shale samples could be identified from the biomarker results with the exception of the sterane and pristane/phytane results. The Floyd/Neal Shale samples have a pristane/phytane average of 1.23, while the Chattanooga Shale samples have an average of 0.34. The Carter sandstone and Pottsville A sand crude oils have averages of 1.46 and 1.53, respectively. A positive correlation was noted between thickness and %TOC levels of the Floyd/Neal Shale. The evidence suggests the Floyd/Neal Shale as the likely source rock of the crude oils in the North Blowhorn Creek and Chicken Swamp Branch oilfields in the Black Warrior basin of western Alabama.

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Petroleum geology