Foam is a promising solution for improving the poor sweep efficiency of gas injection for enhanced oil recovery (EOR), in that foam lowers gas mobility significantly by trapping gas bubbles. Most of oils destabilize foam, the effect of which dominates foam strength when foam is in contact with oil and is key to success of foam EOR, but not yet fully understood. This study focuses on understanding oil displacement by foam in lab scale and providing insights for field-scale applications. We carry out the study from two perspectives: a) X-ray CT corefloods that give data on both saturation and pressure response in a foam displacement and b) data fitting to corefloods results.

Experimental studies are conducted with two types of simplified model oil to avoid confusion of the effect of multi-components of crude oil: hexadecane (C16) that is benign to foam and a mixture of C16 and oleic acid that is greatly detrimental to foam stability. CT scanning provides data on oil saturation (So) and distribution along a core during the corefloods. Such key information relates So to foam dynamics as implied by pressure response, in particular foam generation and propagation suggesting efficiency of oil displacement by foam. Specifically, foam is injected in two ways: co-injection of surfactant solution and gas with the intention to generate foam in situ in the presence of oil and injection of pregenerated foam. The co-injection serves to check the effect of oil on foam generation and propagation (anti-foaming effect) in the displacement. The second way investigates de-foaming effect of oil on foam displacement. The results show that foam generation in situ in the presence of oil is possible only when the oil is relatively benign to foam. When oil is very detrimental to foam, the in-situ generation is very difficult even at oil saturation as low as residual oil saturation. The displacement of pregenerated foam with oil consists of two stages of foam propagation due to change in So. Foam drains down So with a weaker strength due to high So in the primary propagation. In the secondary propagation, foam propagates faster with a larger strength, pushing oil forward like a piston.

Fitting coreflood data is then performed using a most widely used local-equilibrium implicit-texture foam model in CMG STARS™ simulator. We propose a fitting guideline for estimating foam simulation parameters based on steady-state foam flow data with oil in a recent study that does not give data on So. The model parameters estimated using this method serve as an initial guess for finding the optimal parameters to fit the coreflood data in simulation. A simulator for foam simulation in STARS is set up for this purpose. A scheme is then developed to optimize the model parameters in fitting the dynamic data. The challenges and difficulties in the fitting are briefly summarized for future work. ... Read more

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.

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