Depositional environment, sequence stratigraphy, and reservoir quality of the Tonkawa Sandstone in the western Anadarko Basin, Hemphill, Lipscomb and Roberts Counties, Texas
Tussey, Logan Brien
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The Anadarko Basin contains some of the most prolific hydrocarbon reserves in all of North America. A recent USGS publication estimated undiscovered resources across the basin to be 495 million barrels of oil (MMBO), 27 trillion cubic feet of natural gas (TCFG), and 410 million barrels of natural gas liquids (MMBNGL). Pennsylvanian age sandstones contribute substantially to total estimated reserves within the basin. The focus of this study is the late Pennsylvanian Tonkawa Sandstone, the lowermost unit of the Douglas Group, Virgilian Series. Through the integration of core analysis, subsurface mapping, petrographic analysis, and porosity and permeability data, this study presents a detailed analysis of the Tonkawa Sandstone across approximately 1,400 mi² (3,630 km²) in the western Anadarko Basin. The Tonkawa Sandstone is comprised of three high-order transgressive-regressive sequences within one larger, lower-order sequence. Sandstone-body distribution varies greatly, depending upon depositional environments and their associated facies. The Tonkawa Sandstone was deposited in deltaic and estuarine environments with a source area to the northeast. The HST-2 interval, the oldest sandstone-rich sequence in the Tonkawa Sandstone, was deposited in a deltaic environment with a mixed wave and tide-dominated energy regime. The younger HST-3 interval was deposited in a tide-dominated deltaic environment. The youngest interval, TST-3, was deposited in a mixed wave and tide-dominated transgressive estuarine environment. The Tonkawa Sandstone is a sublitharenite to litharenite. Widespread quartz overgrowths minimize variation in reservoir quality among facies. However, more proximal facies display better reservoir quality. Detailed characterization of Pennsylvanian formations such as the Tonkawa Sandstone contributes greatly to the understanding of similar formations within the Anadarko Basin, and other foreland and cratonic basins worldwide.