Okwen, Roland T. (Illinois State Geological Survey, Prairie Research Institute, University of Illinois at Urbana-Champaign) | Frailey, Scott M. (Illinois State Geological Survey, Prairie Research Institute, University of Illinois at Urbana-Champaign)
Historically, deep oil reservoirs with temperatures and pressures above the critical point of carbon dioxide (CO2) are generally preferred over shallower reservoirs in enhanced oil recovery (EOR) and CO2 storage operations because of high recovery and storage efficiencies associated with miscible floods. As a result, shallower reservoirs containing significant volumes of recoverable resource are generally overlooked. However, basins with relatively low geothermal gradients and high fracture gradients, such as the Illinois Basin, can sustain pressures above the vapor pressure of CO2 where CO2 changes from a gas to liquid. Liquid CO2 has fluid properties similar to that of supercritical CO2 and is more readily miscible with oil.
This study evaluates the EOR potential of low-temperature reservoirs based on the performance of a miscible liquid CO2 flood pilot at the Mumford Hills oil field in Posey County, Indiana. About 7,000 tons (6,350 tonnes) of CO2 were injected into a Mississippian sandstone reservoir over a period of 1 year to demonstrate miscible CO2 EOR in low-temperature oil reservoirs. The reservoir model was calibrated with available historical primary waterflood, and CO2 flood pilot data. The calibrated reservoir model was used to simulate different full-field CO2 EOR development scenarios. The projected oil recovery factors range between 10% and 14%, which compares well to the Permian Basin supercritical CO2 flood recovery range of 8% to 16%.
The oil recovery factors from the simulated scenarios suggest that liquid CO2 floods in low-temperature oil reservoirs can achieve an incremental oil recovery similar to deeper, supercritical CO2 floods. Re-evaluating previously overlooked shallow depleted reservoirs as potential candidates for liquid CO2 EOR provides the opportunity to increase the development of these shallow oil reservoirs available for miscible CO2 flooding