The effect of surfactant type, velocity and permeability on CO2 foam under miscible conditions

Miscible gas injection has been widely used worldwide to improve oil recovery. However, problems such as viscous fingering and gravity override undermine its success on a large scale. Foaming of the injected gas mitigates these problems by reducing the mobility of the gas.Past studies using an ionic surfactant to foam CO2 in the presence of decane discovered the presence of three distinct regions based on the fraction of CO2 in the CO2-decane mixture namely; CO2-rich floods where the apparent viscosity increased with the increase in the CO2 molar fraction, decane-rich floods where the apparent viscosity decreased with the increase in the CO2 molar fraction and floods with intermediate CO2 molar fraction where the apparent viscosity was independent of the CO2 molar fraction in the CO2-decane mixture. The foam quality scans showed that the CO2-rich floods and decane-rich floods exhibited both low and high-quality regimes while the floods with intermediate CO2 molar fractions lacked a high-quality regime [1].This behaviour was not fully understood.The effect of the surfactant type on the observed behaviour has been studied in this thesis by using a non-ionic surfactant in the foam quality scans. The results show the presence of the three distinct regions as observed in the previous study with an ionic surfactant. However, this study shows that the quality scans of all the CO2-decane molar compositions exhibit both the high and low-quality regimes. This study also shows that both the low and high-quality regimes are present at high flow rates. In addition, the flow behaviour is shear-thinning in nature and can be modelled by the power law. Furthermore, the transient generation of CO2 foam in the presence of decane at different CO2-decane molar compositions has been investigated. The results show that the generation of CO2 foam in the presence of decane depends on the injected amount of CO2-decane mixture and is independent of the CO2-decane molar composition and quality. Lastly, the effect of permeability on transient foam generation has been tested in low permeability cores and has been compared to foam generation in high permeability cores. The results show that foam generation occurs earlier in low permeability cores. In addition, the low permeability cores are susceptible to damage and blockage especially at high injection rates.Applied Earth Science