Simulation Evaluation of Gravity Stable CO2 Flooding in the Muddy Reservoir at Grieve Field, Wyoming

摘要

Grieve oil field, discovered in 1954, is located in southeastern Wind River Basin, central Wyoming. This Lower Cretaceous, valley-fill and channelized, Muddy sandstone reservoir is a stratigraphic/structural trap with an average structural dip of 15 degrees. Multiple recovery mechanisms have contributed to produce more than 30 million barrels of premium light sweet crude, including gas expansion, down-dip water drive, and re-injection of produced gas into the field's gas cap. The reservoir depth, at 6,900 ft, and oil gravity, 37oAPI, are considered favorable for miscible gravity stable CO2 flooding to enhance oil recovery. Three distinct reservoir lithofacies are identified within the Muddy channel sand at Grieve Field, which are overlain by a low-permeability sandstone interval of bay-head delta deposition. Wettability tests indicate that the reservoir rock is weakly water-wet. A full-field simulation model was developed to simulate the production history and forecast the performance of various CO2 flooding scenarios. The simulation evaluation concluded that gravity stable CO2 flooding can be an effective EOR method for the Grieve Muddy reservoir. Up to 23 MMSTBO could ultimately be recovered by gravity stable CO2 flooding. To repressurize the reservoir to an operation pressure above the minimum miscibility pressure, a cumulative injection of 90 BSCF or more of CO2 would be needed before any production. Total CO2 purchased is estimated to be in the 119 to 188 BSCF range depending on the operation duration and CO2 injection rate. The net CO2 usage efficiency, the ratio between total purchased CO2 and total produced oil, varies from 7.3 to 8.1 MSCF/BO in the simulated cases. The reservoir has potential to sequester more than 145 BSCF of CO2 at the end of CO2 flooding operation.