Investigation of liquid CO₂ sequestration and EOR in low temperature oil reservoirs in the Illinois Basin

Current studies of geologic storage of CO₂, with the exception of CO₂ sequestration in coal beds, focuses on supercritical CO₂, emphasizing the stability of the fluid, solubility of CO₂ in saline formation water and miscibility with crude oil. Likewise, with the exception of very early research, the use of CO₂ to enhance oil recovery (EOR) historically focused on supercritical CO₂ to achieve miscible conditions with crude oil. The only possibility of liquid CO₂ geologic storage is in formations with temperatures less than the critical temperature of CO₂. Due to the naturally occurring geothermal temperature gradient, most all geologic formations currently considered for CO₂ sequestration and EOR exceed the T_cCO2. A research plan has been developed to investigate the use of depleting (mature) oil reservoirs with formation temperatures less than critical temperature of CO₂ to sequester liquid CO₂ and investigate the implications of EOR from the liquid CO₂ displacement process. Relatively higher pressures are required to attain liquid CO₂, which translate to fracture gradients as high as 1.0 psi/ft. However, fracture stimulation data published in early literature and field data from fracture stimulation companies in the Illinois Basin show that fracture gradients of up to 1.0 psi/ft are commonly recorded in the shallower producing horizons of the Basin. Therefore, the pressure requirement may not be a detriment. Because of the liquid/gas phase changes and consequent changes in density and viscosity of CO₂ at subcritical temperatures, low temperature oil reservoirs provide a unique opportunity for liquid CO₂ storage and the application of a novel and innovative EOR-CO₂ cyclic multi-reservoir displacement process within the Illinois Basin.