Simulation evaluation of CO2 flooding in the muddy reservoir

The simulation evaluation concluded that gravity stable CO2 flooding can be an effective EOR method for the Grieve Muddy reservoir. Up to 23 MMBO could ultimately be recovered by gravity stable CO2 flooding. The reservoir has potential to sequester more than 145 BSCF of CO2 at the end of CO2 flooding operation. Prior to the simulation of history matching and CO2 flooding, a four-layer Petrel model of Grieve Muddy reservoir was developed based on the identified facies in the Muddy channel sand and the overlain sandstone interval of bay-head delta deposition. Porosity and permeability distributions of layers generated in the Petrel model were exported to the simulation model. An OOIP estimation of 67 MMBO in Grieve Muddy channel sand has resulted from a simulation history matching based on the full-field material balance. History matching also reveals that about one MMSTBO of oil and 8.2 BSCF of gas have moved down from the overlain low-permeability sandstone interval into the Muddy channel sand interval during the reservoir depletion.

Three representative scenarios are used in this report to demonstrate the performance of gravity stable CO2 flooding under different CO2 injection schemes. To repressurize the reservoir to an operation pressure above the MMP, 90 BSCF or more of CO2 would need to be injected before any production. The initial CO2 demand is estimated to be in the 50,000 to 110,000 MSCF/day range. The repressurization phase could last 2.25 to 6 years, in the simulated cases, depending on CO2 injection volume rates. Total CO2 purchased are estimated to be in the 119 to 188 BSCF range depending on the operation duration and CO2 injection rate. It is estimated that between 20 and 23 MMBO could be produced by a 30-year operation of CO2 flooding while about 80% of the recoverable oil would be produced within the first 5 to 6 years of production. 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.