Adaptability to Enhance Heavy Oil Recovery by Combination and Foam Systems with Fine-Emulsification Properties

Emulsification is increasingly emphasized for heavy oil recovery through chemical flooding. However, whether systems with fine-emulsification (FE) properties significantly outperform conventional ultra-low interfacial tension (IFT) systems, especially under varying water-oil viscosity ratios, remains unclear. In this research, two FE systems and one conventional ultra-low IFT system are compared in terms of their IFTs, emulsification properties, foaming behaviors, and heavy oil recovery (in the form of combination flooding and foam flooding). The results show that FE systems 1# and 2# can generate more stable emulsions of heavy oil than the traditional ultra-low IFT variant 3#. During the first combination flooding, FE systems recover 24.5% and 27.9% of the oil after water, obviously surpassing 21.0% of the ultra-low IFT system 3#; but as this ratio increases to 0.45, those factors become very similar to ones of 33.2%, 34.5% and 32.9%, with the former no longer outperforming the latter. In the second trials of foam flooding, at a lower water-oil viscosity ratio of 0.05, FE foam 1# becomes less effective than the ultra-low IFT 3#, with oil recovery factors of 27.2% and 31.6%, respectively; but foam 2# (combining medium emulsification and ultra-low IFT) remains optimal, with the highest recovery factor of 40.0%. Again, as this ratio becomes 0.45, the advantages of FE systems over the ultra-low IFT system are almost negligible, generating similar oil recoveries of 39.2%, 41.0% and 39.4%.