Abstract

The Late Cretaceous Almond Formation is a lithic-rich, tight-gas sandstone reservoir in Wamsutter field, Wyoming. The Almond has measured porosities of less than 12% and permeabilities that are generally less than 0.1 md. This is the result of significant mechanical and chemical compaction, precipitation of carbonate cements and authigenic clays, and deep-burial cementation by quartz. Despite the advanced diagenesis and poor reservoir quality of this tight-gas sandstone, Touchstone diagenetic modeling was used successfully to simulate rock properties during burial.

Basin modeling and fluid inclusion data were integrated with Touchstone™ simulations to constrain the timing of petroleum charge into the reservoir. Model results indicate that the Almond was initially charged by liquid petroleum, when the reservoir retained high porosity and permeability. Subsequent gas charging flushed most of the liquids from the system as the reservoir continued to experience porosity and permeability reduction from continued quartz cementation.

The Almond Touchstone model was applied to 15 well locations throughout the field, ranging from areas of low thermal stress to high thermal stress. A comparison of Touchstone-predicted permeability and standard thermal stress yielded a correlation that was used to build a pseudopermeability reservoir quality risk map across the Wamsutter area. A comparison of this map with historical production data demonstrates that the map successfully predicts areas of enhanced well performance. The method used to build this risk map may be applied elsewhere as a quick means of high grading areas of risk during field development.

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