Sedimentology and Reservoir Characterization of the Wagon Wheel Formation from Seismic, Log, and Core Data in Pinedale Field, Wyoming
Mark A. Chapin, Andrew Govert, 2014. "Sedimentology and Reservoir Characterization of the Wagon Wheel Formation from Seismic, Log, and Core Data in Pinedale Field, Wyoming", Pinedale Field: Case Study of a Giant Tight Gas Sandstone Reservoir, Mark W. Longman, Stephen R. Kneller, Thomas S. Meyer, Mark A. Chapin
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The giant Pinedale gas field in the Green River Basin of Wyoming produces from up to 6000 ft (1800 m) of the Upper Cretaceous fluvial sandstones of the Lance Formation, the Upper Mesaverde Group, and the Paleocene Wagon Wheel Formation. The Wagon Wheel Formation is approximately 1300 ft (400 m) thick and differs in character from the underlying Lance and Mesaverde Formations in having conglomerates and significant feldspathic components. This lithologic change has previously been attributed to the unroofing of the crystalline core of the Wind River Mountains. The distinct lithology and mineralogy causes different log and rock property relationships than those seen in the Lance and Mesaverde.
A recent core in the Wagon Wheel Formation has allowed modern core analysis techniques to be applied, increasing our understanding of the reservoir characteristics for this interval. Porosity and permeability are higher in sandstones and conglomerates of the Wagon Wheel Formation as compared to the sandstones of the Lance Formation. Upper and lower intervals within the Wagon Wheel Formation have distinct lithologies and are separated by an unconformity. A distinct gamma-ray log shift, the “gamma-ray marker,” is present at the unconformity and is caused by an increase in potassium and thorium related to increases in feldspar and chlorite above the unconformity. The lower interval contains both lithic sandstones similar to the Lance and also feldspathic conglomerates. The upper interval contains feldspathic coarse sandstones and conglomerates but is dominated by greenish-gray debrites containing poorly sorted mixtures of chlorite-rich clay, sand, and pebbles. The upper interval is water bearing, whereas the lower interval contains and can produce gas, albeit with higher water saturation than that found in the Lance Formation.