Study Year: 2022
Characterization and Simulation of Reservoirs in the Muddy Formation: Hirsch Field Area, Powder River Basin, Wyoming

Executive Summary

The Lower Cretaceous Muddy Formation is a significant oil-bearing interval in the Powder River Basin. Most traps in the formation are stratigraphic in nature, with compartmentalized flow units comprising fine-grained to very finegrained sandstones deposited within up to six separate members. Primary production from typical Muddy reservoirs results from a robust solution gas drive with little produced formation water. Some fields, particularly those producing from the lower members deposited in fluvial or estuarine environments, are sensitive to the introduction of foreign water, making waterflooding problematic. Those fields producing from the upper members, deposited in marine environments, tend to react to water-flooding much more favorably.

Recently acquired seismic data indicated a narrow band of relatively thick Muddy sandstone in an area about twenty-four miles northeast of the town of Gillette and immediately west of Gibbs Field, which produces from the Permian/ Pennsylvanian Minnelusa Formation. Based on these data, the operator drilled and completed three widely separated wells in the Muddy Formation during 2018 and 2019, which, at this writing, are still on primary production.

Reservoir mapping indicates the Muddy reservoirs in the Hirsch area are compartmentalized and were deposited in estuarine and shallow marine environments. There appears to be good potential for additional wells. Simulation modeling suggests that these reservoir compartments are not being equally drained and that an injection program would improve the recovery factor in each of the reservoir compartments. Several different scenarios were examined, which illustrates the type of methodology that can be used to determine an optimal development plan that maximizes profit.

Acknowledgements & Credits: Stephen T. Whitaker and Shuiquan Li