The role of emulsification and IFT reduction in recovering heavy oil during alkaline-surfactant-assisted CO2 foam flooding: An experimental study

A comprehensive experimental study is performed to investigate the performance of alkali-surfactant (AS) assisted foam flooding as a means of tertiary Enhanced Oil Recovery (EOR) process in post-CHOPS reservoirs (i.e., reservoirs where cold heavy oil production with sand has been employed) and to elucidate how AS-assisted foam (i.e., foam stabilized by AS solutions) EOR of heavy oil is affected by oil-water interfacial tension (IFT) reduction and emulsion formation. Three surfactants (S) and the corresponding alkali-surfactant (AS) solutions with different oil-water IFT and emulsification properties are employed. The stability of foam in the presence of the solubilized oil, the coalescence time of an oil droplet at CO2-water interface (tc), together with the stability and heavy oil viscosity-reducing ability of oil-laden foam (OLF) for different chemical solutions are assessed. The results show that CO2 foam generated by AS(2) solution (with non-ultra-low IFT and the best emulsion stability) in the presence of oil solubilized in micelles is the most stable. Meanwhile, AS(2) OLF exhibits the longest tc and performs the best in improving heavy oil flowability, implying that the importance of emulsion stability and the pseudoemulsion film stability on the OLF stability. Micromodel experiments are performed to help rapidly identify promising AS formulation and to reveal the pore-scale mechanisms involved during AS-assisted foam EOR processes. It is shown that the emulsion stability of chemical solutions plays a key role in recovering heavy oil; despite the greater IFT, due to the formation of more stable oil-in-water emulsion, and the resulting better mobility control, as well as wettability alteration towards more water-wet state, AS(2)-assisted CO2 foam is found to be more favorable for recovering heavy oil (mu(o) = 1850 cP) in post-CHOPS oil reservoirs.

Automated summary

This study investigates the performance of alkali-surfactant (AS) assisted foam flooding as a tertiary Enhanced Oil Recovery (EOR) process in post-CHOPS reservoirs and how it is affected by oil-water interfacial tension reduction and emulsion formation. The results show that CO2 foam generated by AS(2) solution is the most stable, and AS(2) OLF performs the best in improving heavy oil flowability.