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Influence of Fractures on Gas Production at Hay Reservoir Field, Sweetwater County, Wyoming

Pasternack, Ira
Colorado School of Mines, Golden, CO

Hay Reservoir is the second largest upper Cretaceous Lewis Shale field in the Green River basin with cumulative production from overpressured, tight-gas sandstones totaling more than 150 BCFG. The excellent core control available at Hay Reservoir provides a unique opportunity among Lewis Shale fields for reservoir characterization.

Production at Hay Reservoir is primarily from a single lobe-shaped sandstone interval, interpreted as a series of amalgamated sediment gravity flows deposited within a deep-water setting. Laramide uplift of the sandstone depositional toes resulted in the stratigraphic trap configuration responsible for the Hay Reservoir accumulation.

Petrographic studies suggest that porosity development within the very fine- to medium-grained arkosic sandstones is dominantly from the secondary dissolution of feldspar, lithic and carbonate grains. Porosity, permeability and production at Hay Reservoir all appear to improve in structurally updip positions.

Natural fractures have been identified in the majority of the Hay Reservoir cores. These fractures may have had a role in controlling secondary porosity development or controlling production variations at Hay Reservoir field.