17-7 Chemostratigraphy of the upper Devonian Woodford Formation from the Permian Basin, Texas: A deeper look into the redox structure of the Tobosa Basin

Session: One Century of Oil and Gas in the Permian Basin

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Abstract:

Over the past decade there has been renewed interest in the mudrocks or black shales of the Permian Basin including the Permian Wolfcamp Formation, the Mississippian Barnett Formation, and the Devonian Woodford Formation. The fine-grained, organic-rich sediments within these formations have long been considered excellent source rocks to the extensive petroleum reservoirs found throughout the Permian Basin. With the widespread implementation of hydraulic fracturing technologies these unconventional reservoirs have generated significant interest among energy professionals. Energy dispersive X-ray fluorescence (ED-XRF) has emerged as a standard tool for evaluating these deepwater mudrocks. Chemostratigraphic trends in redox sensitive trace metals such as Nickel (Ni), Uranium (U), Vanadium (Va), Molybdenum (Mo), and others allow for the identification of paleoredox gradients associated with sediment deposition across paleo-depositional environments. Enrichments in these redox sensitive trace metals generally correlate with high total organic carbon (TOC) content and, thus, high hydrocarbon potential. 

This study presents new geochemical data from two cores taken within the upper Devonian Woodford Formation from the Permian (Tobosa) Basin. ED-XRF data was collected at ~ 6 cm (0.2 ft) intervals from the Fasken Fee BK #1514 core from Ector County, TX, and the Hentz Family 7-1 core from Winkler County, TX. The new ED-XRF data was then compared with previously reported data from the Pioneer Reliance Triple Crown #1 core from Pecos County, TX. Log data from more than 80 wells penetrating Devonian strata from across the basin were used to correlate between wells in this study and to create formation thickness map of the Woodford Formation. The Woodford Formation of the Tobosa Basin can be divided into a lower, middle, and upper Woodford interval based on gamma ray logs and chemostratigraphic trends that span the Late Devonian. Geochemical profiles obtained from these cores demonstrate widespread periods of anoxic to euxinic conditions during deposition of all three intervals of the Woodford Formation. Variable enrichments in redox sensitive trace metals observed between the cores suggests the presence of a strong chemocline with potential shuttling of redox sensitive metals within the Tobosa Basin. These findings are consistent with paleoredox conditions observed in other sedimentary basins of similar age across Laurentia. 

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-6556

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