Assessing the Potential for Improved Oil Recovery in Oilfields with Sparse Data: The Muddy Formation at Rozet and Windmill Fields, Powder River Basin, Wyoming

At Rozet Field, the lack of abundant core analyses or modern logs necessitates the adoption of more assumptions than usual in order to estimate OOIP and remaining recoverable reserves. Two different methods for calculating the recovery efficiency of the waterflood were applied withinnine 5-spot patterns resulting in maximum rates of 40% and 30% respectively. Average recovery factors in the combined 5-spot patterns are 27.5% and 24.4% respectively. Both values indicate
the waterflood is probably not as effective as it could have been when compared to similar fields producing from the Muddy Formation.

The calculated OOIP for the Muddy Formation at Rozet is about 74.7 million barrels, of which a little over 19 million barrels have been recovered. The recovery factor for the field is then about 25.5%. If a 40% recovery factor is achievable with an efficient waterflood, then the remaining recoverable oil reserves from the Muddy Formation at Rozet Field are approximately 10.8 million barrels. This magnitude of a target should warrant further investment in improved and enhanced recovery methods there.

At nearby Windmill Field, secondary recovery has yet to be implemented in the Muddy reservoir. Wireline log suites containing porosity logs in this field enable more confidence in the geologic mapping and OOIP calculations than at Rozet. Cumulative oil production there is 677,735 barrels, resulting in a recovery factor of about 14.8%. Assuming the clay content does not vary significantly from that observed at the adjacent Rozet Field, a well-designed waterflood should be effective at increasing production in Windmill Field. If a recovery factor of 40% could be achieved by implementing secondary recovery efforts there, it could result in the production of an additional 1,157,465 barrels of oil.