Experimental evaluation of high performance EOR surfactants for a dolomite oil reservoir
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An experimental study was done to evaluate promising EOR surfactants based upon a fast, low-cost laboratory screening process that is highly effective in selecting the best surfactants to use with different crude oils. Initial selection of surfactants was based upon desirable surfactant structures determined from previous surfactant research both at the University of Texas and elsewhere. Phase behavior screening helps to quickly identify favorable surfactant formulations. Salinity scans are conducted to observe equilibration times, microemulsion viscosity, oil and water solubilization ratios and interfacial tension as well as to identify problems with macroemulsions and other undesirable behavior. Co-surfactants and co-solvents are included to minimize gels, liquid crystals and macroemulsions and to promote rapid equilibration to low-viscosity microemulsions. Branched alcohol propoxy sulfates and internal olefin sulfonates have been identified as good EOR surfactants using this screening process. One of the best formulations was tested in both sandstone and dolomite reservoir cores and found to give excellent oil recovery and low surfactant retention. The formulation C16-17[PO]7SO4, C15-18IOS, sec-butanol and FP3330 HPAM polymer when used with a good salinity gradient and good mobility control reduced the residual oil saturation to only about 0.03 in both Berea sandstone and a West Texas dolomite at 38 C. This result indicates that there is a very high potential for surfactant-polymer enhanced oil recovery in carbonate oil reservoirs using the same surfactants as suitable for sandstone oil reservoirs. This is a remarkable and highly significant development in chemical EOR.