X-ray Fluorescence and Total Organic Carbon Analysis of Delaware Basin Ordovician Age Sediments in the Ellenburger and Simpson Groups of West Texas
Cuyler, Joshua Robert
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Ordovician age hydrocarbons have been drilled in the Permian Basin of West Texas since the early 1940s and have produced over a billion barrels of oil with additional natural gas. The source rock for these previously drilled Ellenburger Group reservoirs has been suggested to be the Simpson Group shales, but limited total organic carbon studies and no x-ray fluorescence analysis has been performed on the Permian Basin Ordovician rocks to determine the overall lithology and trace element enrichment relative to total organic carbon to substantiate this statement. The majority of Ordovician hydrocarbon production has occurred in faulted and structural traps in the Ellenburger, but the hydrocarbons have a different hypothesized source due to generally low total organic carbon within this group. Trace element enrichments can serve as indicators of the presence of organic material and paleoredox conditions. This study utilizes x-ray fluorescence elemental data and total organic carbon data from Permian Basin Ordovician sediments to analyze general rock lithology and to understand whether biologically- and paleoredox-sensitive trace elements coincide with total organic carbon, and if so, can these similarities give insight to the organic enrichment of these sediments and the paleoredox conditions present during their deposition. The findings of this study suggest that the Simpson Group reflects a depositional environment with intermittent layers of sandstone, green shale, black shale, red shale, and a large percentage of carbonate suggesting a shallow water marine environment. The majority of trace elements that serve as useful proxies for total organic carbon within these sediments are mostly associated with the detrital shale influx and are not associated with biological activity or paleoredox conditions. The majority of the total organic carbon values for the Simpson Group and Ellenburger Group suggest a poor (<0.5 wt. % total organic carbon) source rock with limited potential to generate hydrocarbons though fair (.5-1 wt. % total organic carbon) to good (1-2 wt. % total organic carbon) values are present in a limited number of samples. X-ray fluorescence data indicates the presence of trace element enrichments in some samples, but no clear correlation with total organic carbon is recognized.