New surfactant developments for chemical enhanced oil recovery

Recent advancements in surfactants for chemical enhanced oil recovery (EOR) are presented. For oils with a high equivalent alkane carbon number (EACN), surfactants with very large hydrophobes are needed to obtain the ultra-low interfacial tensions needed to reduce the residual oil saturation to nearly zero. The need increases at high temperature. Furthermore, these large hydrophobes need to be branched to promote formation of microemulsions with low to moderate viscosity as opposed to gels or other viscous structures that cause high surfactant retention. We show that such surfactants can be made from more than one type of hydrophobe in the form of either alkoxy sulfates or carboxylates. The carboxylates have the advantage of better stability at high temperature. Both the sulfates and carboxylates can be easily tailored to specific reservoir conditions and oils by adjusting the number of ethylene oxide (EO) or propylene oxide (PO) groups in the surfactant. A new correlation has been developed using an extensive data set taking into account the effects of PO number, EO number, temperature, brine salinity and the EACN of the oil on the optimum hydrophobe size. These new developments have enabled us to address a much wider range of conditions of oil characteristics, reservoir temperature, salinity and hardness level. Furthermore, the new surfactants are competitive in cost with previous EOR surfactants. Thus, these new developments have greatly advanced the commercial potential of chemical EOR.