Experimental Evaluation of a Surfactant/Compound Organic Alkalis Flooding System for Enhanced Oil Recovery

Monoisopropanolamine (MIA) and monoethanolamine (MEA), which are two kinds of organic alkalis, present favorable potential for enhanced oil recovery. When MIA and MEA are respectively applied, the minimum oil/water interfacial tension (IFT) can be reduced to about 1 mN/m, the crude oil can be emulsified, and the originally oil–wet sand surface can be altered to weak water-wet status. To display the synergistic effect of surfactant and organic alkalis, a surfactant/compound organic alkalis (MIE/MEA) flooding system (SMM), which consists of 0.10 wt % SDBS, 0.15 wt % MIA, and 0.10 wt % MEA, is screened. This system can reduce the minimum oil/water IFT to an ultralow value which contributes to the emulsion stability. Results of sandpack flooding tests indicate that although the incremental oil recovery can be continuously enhanced with the increase of the SMM slug size, there is an optimal injection size (0.8 PV in this study) when the expense is taken into consideration. As for the effect of the injection type, the highest incremental oil recovery (21.86% OOIP) is achieved when organic alkalis (MIA/MEA) are simultaneously injected with the SDBS. During the SMM flooding, emulsification is a crucial flooding mechanism, and most of the incremental oil is extracted in the form of emulsified oil droplets. Moreover, the injection rate is optimized (0.5 mL/min) for the SMM flooding system to achieve a satisfactory incremental oil recovery.