Evaluating Foam Stability Using Tailored Water Chemistry for CO2 Mobility Control Applications

Generating in-situ foam with CO₂ is regarded as one of the most promising techniques to overcome gas mobility issues and improve sweep efficiency in EOR processes. Gravity override, viscous fingering and channeling through permeable zones are the major limiting factors that can impair the efficiency of gas floods. Generating strong and stable foam while injecting CO₂ is one way to achieve in-depth conformance improvement in the reservoir.

The foams are generated by mixing the injection gas with injection water containing surfactant in the laboratory. A tailored water chemistry (formulated low salinity water) has been evaluated in comparison to using typical high salinity injection water in surfactant solution to determine its overall effect on the produced foam. Using foam rheology apparatus, the foam stabilization factors were analyzed and quantified by measuring the foam-life and the bubble sizes of different surfactants in varying salinity water solutions.

The results clearly demonstrated that the use of tailored water chemistry improved the stability of produced foams when compared to high salinity water. Low salinity tailored water chemistry solutions resulted in a longer lasting foam, by almost 1.5-3.0 times depending on the surfactant type. The bubble sizes were found to be much smaller in the tailored water chemistry when compared to high salinity water. Both longer foam-life and smaller bubble sizes are indicative of better, stronger and more stable foam. The foam rheology results also showed that the produced foams with the tailored low salinity water are of higher apparent viscosity when compared to those obtained with high salinity water.

This experimental study, for the first time, demonstrated the substantial improvements in the foam stability by using a tailored water chemistry. Such huge foam stabilization improvements obtained with tailored water chemistry has the promising potential to increase the apparent viscosity of injected gas and eventually EOR.