Steam injection is widely used enhanced oil recovery technique for heavy oil extraction. However, environmental and economic drawbacks of steam generation make the chemical additive-steam injection processes more favorable than steam injection alone. In this study, the performance of surfactant-steam flood process were investigated for heavy oil recovery and a quick recipe was proposed for the right surfactant selection through dielectric constant measurements.
Experiments were conducted on two heavy oil samples with different API gravity (12.09° and 11.56°) and viscosity (10,100 cP and 208,500 cP). Three anionic surfactants with same polar head group (sodium sulfate) but with different nonpolar tail length [long (SDS), moderate (SDeS), and short (SOS)] were selected to be tested. The crude samples and their SARA (Saturate, Aromatic, Resins, and Asphaltenes) fractions were blended with surfactant solutions at their critical micelle concentration (CMC). Interaction of crude oils, crude oils' non-polar fractions (Saturates and Aromatics) and crude oils' polar fractions (Resins and Asphaltenes) with surfactant solutions were visualized under optical microscope. An innovative and quick method, dielectric constant measurements were used to quantify indirectly the polarity of the blends. These measurements were used to determine the best surfactant candidates to recover each oil samples and accuracy of this new method was validated through optical microscopy images.
Microscopic images revealed asphaltenes have the higher contribution in the formation of micro-emulsions. It is observed that the polar-polar interaction of asphaltenes with resins adversely affected the surfactant performance due to reduction in overall polarity. We found that as the dielectric constant increases, the polarity of the oil/surfactant blends (microemulsions) increases which indicates that polar-polar interaction between oil/surfactant is minimized and the effectiveness of surfactants is maximized. Microscopic images were used to confirm this finding and for the blends having higher dielectric constants, minimum interaction of resins with surfactants and lower asphaltene aggregation for the same crude oil-surfactant blends were observed.
Our results offer that dielectric constant measurements can be used as an innovative and easy surfactant screening method.