Effect of Surfactant Structure on Phase Behavior of Alkylxylenesulfonate/Crude-Oil/Brine Systems

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Abstract
Summary: One of the major criteria for designing surfactants for micellar flooding is their effectiveness in stabilizing a middle-phase microemulsion under the conditions of the candidate reservoir. We studied the performance of linear alkyl-o-xylenesulfonates (Enordet™ LXS) with equivalent weights ranging from 345 to 472 with well-defined molecular structures. We used information about a previously described quantitative relationship between the mole fractions of the individual surfactant components and their effect on the optimal salinity in surfactant/crude-oil/brine systems. This relationship makes it possible to calculate blend compositions that have near-optimal properties with respect to the required salinity at which the three phases—i.e., oil, microemulsion, and brine—occur. In this work, however, we have further refined the correlation between surfactant structure parameters and performance by including the effect of factors such as the mole-fraction distribution, the aromatic substitution pattern of the alkylxylenesulfonates, and the presence of the cosurfactant Enordet 3ES. We studied the performance aspects of optimal salinity, the solubilization of crude oil and brine at the optimal salinity, and the sensitivity to divalent ions expressed as the "effectiveness ratio." The data generated in this study make it possible to adjust the properties of a surfactant blend in relation to the characteristics of a crude-oil reservoir, thus minimizing the need for trial-and-error experiments.