Abstract

For miscible displacement under most reservoir conditions, due to the very low viscosity of the CO2 phase, poor volumetric sweep efficiency is a critical weakness of CO2 enhanced oil recovery (EOR). In this paper, a dynamic process for generating nanoparticle-stabilized CO2 foam is presented, which is expected to reduce CO2 mobility during CO2 EOR. This paper also describes the factors of nanoparticle concentration, CO2/brine volumetric ratio, and total injection rate effects on dynamic CO2 foam generation and foam mobility.

Dynamic supercritical CO2 foam was generated by the shearing of supercritical CO2 and nanoparticle dispersions in a glass- bead packed column. The foam image was observed in an online sapphire tube. Particle size was determined to be in the range of 60–90 nm. The experimental results showed that stable dynamic foam was generated at a shear rate higher than 1419s‒1 at 1500 psig and 25°C. The pressure differentials along the glass bead packed column and capillary tube were used to characterize the CO2 foam mobility and the corresponding apparent foam viscosity. It was found that the yield shear rate increased from 1419s‒1 to 3312s‒1 as the injection rate increased from 3.0ml/min to 7.0ml/min, and the apparent foam viscosity with nanoparticle dispersion was 1.5 to 2.5 times higher than that without the dispersion. The corresponding mobility was nine times higher. With increasing nanoparticle concentration, the normalized mixture viscosity increased and related mobility decreased. Furthermore, the apparent viscosity decreased slightly as the CO2/brine ratio was varied from 2 to 11 at the constant flow rate of 6ml/min.

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