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The giant Pinedale gas field in the Green River Basin of Wyoming produces from a 5500–6000 ft (1700–1800 m) interval of Upper Cretaceous fluvial sandstones in the Lance Formation, the Upper Mesaverde interval just above the Ericson Sandstone, and the Paleocene Wagon Wheel Formation. Typical porosities for the field are <10% with micro-Darcy permeability. Over 4000 ft (1220 m) of core have been examined to better characterize facies for correlation to rock properties for reservoir modeling and decisions on optimizing field development.

The main types of reservoir sandstones are river channel deposits and overbank splay or sheet sands. Channels display fining-up sequences typical of river bar deposits. These sequences have been subdivided into four facies: (1) channel base lags, (2) lower bar or active thalweg fill, (3) upper bar, and (4) soil-modified bar top and abandonment fill. Splay sandstones are typically finer grained and more cemented, with lower reservoir quality. Overbank mudrocks display pervasive features consistent with incipient soil formation, including roots, peds, and insect burrows.

Despite an overall similarity in facies character, there are variations in facies and stacking patterns both vertically and laterally around the anticline. The Upper Mesaverde interval has fewer sandstones; thinner, dominantly single-story channels; thicker intervals of splay sands; and more carbonaceous and burrowed overbank mudstones. This suggests a higher accommodation, lower coastal plain setting with poorly drained floodplains. The Lance Formation contains thicker channel deposits with varying amalgamation and more multistory channels, indicative of intervals with a higher ratio of sediment supply to accommodation. The upper Lance Formation also has more oxidized mudstones and calcite nodules in floodplain deposits, indicating better drainage and/or possibly drier climate.

Log response is sensitive to many subtle geologic features, such as cemented zones and mud-clast lags, and can be used to differentiate depositional facies. There is a good correlation between porosity and permeability in appropriately stress-corrected core measurements. There is a clear depth relationship to porosity and permeability with the Upper Mesaverde sandstones having lower porosity and permeability than the Lance sandstones. Despite significant compaction and cementation leading to low porosity and permeability, there is a good correspondence of core and log petrophysical properties to facies with larger grain size and higher energy facies having generally greater porosity and permeability. Porosity and permeability within channel facies are broadly similar between single-story and multistory channels, but multi-story channels have thicker intervals of the highest quality channel facies because of erosional amalgamation. Relationships regarding story thickness, facies characterization, porosity, and permeability are used to construct detailed numerical models to study various aspects of field development decisions.

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