The Middle-Upper Ordovician Simpson Group of the Permian Basin: Deposition, Diagenesis, and Reservoir Development

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Middle Ordovician Simpson Group rocks were deposited during a period of overall sea-level rise and marine transgression, following an extensive hiatus and the development of an irregular karst topography on the underlying Lower Ordovician Ellenburger carbonates. Simpson Group production primarily stems from three sandstone units situated in the middle of the group. These sandstones were sourced from eroding highs to the north and east and were transported to the cratonic margins by eolian and fluvial processes. They represent lowstand and/or early transgressive deposits of three third-order sequences. Non-reservoir shales and clay-rich carbonates, deposited during maximum flooding, along with normal marine and restricted carbonates deposited during highstand, comprise the balance of the sequences. Carbonate sequences are present both above and below these three reservoir-bearing sequences, resulting in a total of five third-order Simpson Group sequences within Sloss's second-order Tippecanoe I sequence.

The three sandstone members of the Simpson Group—the Connell, Waddell, and McKee—occur at the base of the Oil Creek, McLish, and Tulip Creek Formations, respectively, arranged from oldest to youngest. Additionally, the Simpson Group includes the underlying Joins and overlying Bromide carbonate formations. These Simpson rocks were deposited during the Rangerian to middle Turinian stages of the Whiterockian and early Mohawkian series (North American) of the Middle to Upper Ordovician.

Productive sandstones within the Simpson Group are typically quartz-rich and range from 20 to 50 feet in thickness. Porosity is commonly reduced by pore-filling carbonate cements and pore-lining clays. While the Simpson play exhibits limited production in the Permian Basin of Texas and New Mexico compared to Oklahoma, production in both areas primarily occurs from structural traps. Despite favorable depositional conditions, stratigraphic traps have not been widely explored. Moreover, the Simpson Group plays an important non-reservoir role in Permian Basin production, as its organic-carbon-rich shales are likely the source of the Ordovician oil found in many Central Basin Platform area reservoirs, including the Lower Ordovician Ellenburger. The Simpson Group is thickest in Pecos and Reeves Counties in Texas, thinning to the north and east and being absent over most of New Mexico, except for the southeasternmost part, and at the eastern edge of the Permian Basin region.


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