The performance of CO2 IOR on low-permeable chalk was tested in two reservoir condition experiments modelling the Syd Arne oil field of the Danish North Sea. Conditions were Pfluid=380 bar, NOB=120 bar, and T=115 °C. A core sample with porosity=29.4 %, and kg=1.6 mD was used. Fluids were recombined live crude oil, simulated formation water, and pure supercritical CO2. The oil-CO2 system was above the minimum miscibility pressure.
Starting at an Swi of 0.147 PV, a water-flooding was conducted that resulted in the production of 0.597 PV of oil and an Sorw of 0.256 PV. This represents the end-point for the water-flooding experiment, and was the starting point for the CO2-flooding experiment. CO2-flooding produced only water until injection of 0.476 PV of CO2 where breakthrough of a miscible oil+CO2 phase occurred, followed by a sharp rise in production of oil+CO2 without detectable fingering. At breakthrough the miscible oil+CO2 phase had high contents of hydrocarbon, which gradually decreased. After injection of 1.51 PV of CO2, the cumulate oil production during CO2-flooding was 0.197 PV and the sample had reached an SorCO2 of 0.059 PV. After this no further oil production occurred. The efficient sweep of the CO2-flooding is attributed to increased viscosity of the miscible oil+CO2 phase and to transverse layering within the sample. Corrosion and compaction of the rock sample were insignificant. Permeability change was absent within the precision of the experiment.
The experiment indicates a potential for CO2 IOR to produce significant amounts of oil from low-permeable chalk, even after a water-flooding operation. It further indicates adverse effects from corrosion and compaction to be limited.