Displacement efficiency of supercritical CO2 flooding in tight carbonate rocks under immiscible conditions

Carbon dioxide flooding is currently being investigated as possible EOR processes in UAE candidate reservoirs. The major reasons for selecting CO ₂ flooding as an EOR process were low permeability and heterogeneity of these reservoirs that resulted in poor response to traditional water injection. In this study, immiscible CO₂ displacement efficiency of low permeability carbonate rocks of a selected UAE field is evaluated experimentally. Laboratory tests were conducted on seven tight cores extracted from the selected oil field with a permeability range from 0.16 to 11.99 mD and porosity range from 7.72 to 18.63%. The effects of pressure, permeability, and initial oil saturation on the residual oil saturation after flooding at immiscible conditions were investigated in this study. The pressure was varied from 1600 to 4000 psi, and permeability was varied from 0.16 to 11.99 mD at constant pressure of 1600 psi. All runs were conducted at isothermal condition of 127°F while the initial oil saturation ranged from 0.334 to 0.79% pore volume. Experimental results indicated that immiscible supercritical (SC) CO2 is capable of mobilizing oil in the very low permeability environment (0.16 mD) with reasonable displacement efficiency. Also, higher displacement efficiencies could be obtained if we start the flooding process earlier, i.e. at higher oil saturation, as there is a critical starting oil saturation required to optimize the displacement efficiency. Side effects from the process are that notable asphaltene precipitation was observed and SC CO2 injection in limestone cores results in the precipitation of calcite in the downstream area. Scanning Electron Microscope (SEM) was used to provide accurate description of pores prior and post CO₂ flooding experiments and Energy Dispersive X-Ray Spectrometer (EDS) was used to evaluate the composition of the deposited asphaltene.