Performance of extended surfactant and its mixture with betaine surfactant for enhanced oil recovery in sandstone reservoirs with low permeability

Carboxy betaines CnZC (where n represents the carbon number of the alkyl chain, n = 12,14 and 16) and extended surfactant C16P3E6S were combined to assess their potential application for enhanced oil recovery (EOR) by investigating the surface properties, interfacial properties and emulsifications of the single and compounded surfactants. The results demonstrated that four surfactants with favorable water solubility exhibited better surface properties. Among them, the mixture of betaine surfactant C14ZC and sulfonate surfactant C16P3E6S displayed a synergistic effect in reducing interfacial tension (IFT). The solution with C14ZC mole fractions of 60 % and 50 % possessed an ultra-low IFT (10-3 mN/m order of magnitude) at 10 % NaCl whose emulsification rates of oil in brine for mixtures exceeded 90 % at 4 % NaCl. Notably, the emulsion droplet diameter was smaller compared to other salinity conditions, indicating that the combination of C16P3E6S and C14ZC enhanced emulsion stability, correspondingly ultra-low IFTs at both the oil-emulsion and emulsion-water interfaces. Coreflooding experiments revealed that the depressurization rate for the optimized surfactant system (with a molar fraction of C16P3E6S/C14ZC = 2:3) with superior emulsification properties, effectively abilities of reduced IFT, increased capillary number and lower adsorption loss was 26.7 % and its EOR was 20.4 %, confirming its favorable displacement performance and potential application in medium to high salinity reservoirs.