CO2-water drainage relative permeability is usually measured in laboratory using a three-stage unsteady-state flooding on cores. This three-stage flooding involves injecting water, then CO2-saturated water, and finally water-saturated supercritical CO2. The injection of CO2-saturated water has been previously found to generate fines due to mineral dissolution. The generated fines can flow with injected fluids and cause pore blockage.
This paper examines the effect of fines migration and mineral reactions on CO2-water drainage relative permeability measurements, using a sintered glass core and eight Berea sandstone cores. Three-stage and two-stage flooding are performed on the cores. Three-stage flooding sequence is same as literature. Two-stage flooding involves injection only of water and then water-saturated CO2, to avoid the chemical reactions brought about by CO2-saturated water injection and thereby reduce mineral reactions. Pressure difference across the cores and volumes of water produced are recorded. These data are used to generate CO2-water drainage relative permeability functions.
Inductively Coupled Plasma Optical Emission Spectrometry (ICP-OES) analysis of the produced water and Scanning Electron Microscopy (SEM) images of the cores confirm mineral reactions occurred during CO2-saturated water injection in Berea cores. For Berea cores, CO2 relative permeability is reduced (by 21% to 48%) during three-stage flooding when CO2-saturated water is injected. The reduction in CO2 relative permeability is found to be a function of water salinity and pore volumes of CO2-saturated water injected. Experiments performed on the glass core suggest that the error in CO2 relative permeability caused by the absence of CO2-saturated water is negligible. Therefore, we propose that CO2-saturated water be omitted during CO2-water drainage relative permeability measurements.
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