Efficiently exploiting the natural gas from the Upper Cretaceous Mesaverde Formation in the Wamsutter area of southern Wyoming has depended on new applications of existing technology. An understanding of trapping conditions and reservoir performance has required determination of reservoir rock types based on depositional environments and regional stratigraphy.

Two types of traps were discovered: (1) updip shale-outs of sandstones in the upper Almond and Ericson Formations, and (2) increased gas and water interfacial tension in the lower Almond Formation on the cooler updip flanks of the area.

Reservoir performance is strongly influenced by rock types and reservoir geometries. These are controlled by depositional environments which were determined early in the play by examination of slabbed cores. Productive sandstones were observed from the following environments: nearshore marine (upper Almond), high-energy fluvial (Ericson), and low-energy fluvial (lower Almond). Upper Almond sandstones have the best production because of generally good pore geometry and great lateral continuity. Ericson sandstones produce at high rates in a few areas, but tend to produce water because of their great lateral extent. In contrast, lower Almond sandstones rarely produce water, but only flow gas at low rates due to their poor pore geometry and very limited extent.

Drilling plans, completion procedures, and formation evaluation methods all were influenced by the understanding gained from this integrated geologic and petrophysical study.

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