Salinity tolerance, surfactant formulations

Salinity Tolerance. As the petroleum reservoir salinity can be very high, the surfactant formulations should be designed for high salt tolerance. The widely used petroleum sulfonates for enhanced oil recovery exhibit relatively low salt tolerance in the range 2-2.5% NaCl concentration, and even smaller for the optimal salinity. The presence of divalent cations in the brine decreases the optimal salinity of surfactant formulations (44). 

Bansal, V.K. and Shah, D.O., The Effect of Ethoxylated Sulfonates on Salt Tolerance and Optimal Salinity of Surfactant Formulations for Tertiary Oil Recovery.,... 

Salinity Salinity plays at least two important roles, namely it maintains the integrity of the reservoir and it balances the physicochemical environment so that surfactant formulation stays close to optimal. Thus, ultra-low interfacial tension and oil solubilisation are very sensitive to salinity. Mixing of the surfactant slug with connate water may alter the surfactant formulation mainly due to dilution and to the incorporation of new electrolytes to the formula. Adsorption and desorption of electrolytes, particularly divalent cations, onto or from solid materials such as clay, will also change the salinity of the aqueous phases to some extent and may cause surfactant precipitation, which is however not always an adverse effect [151]. In order to attenuate the undesirable salinity effects on formulation, surfactants able to tolerate salinity changes [109], high salinity [150] and the presence of divalent ions [112] maybe used. 

Ethoxylated Sulfonates The condensation of fatty alcohols and ethylene oxide yields non-ionic sufactants, which are low emulsifiers and low foamers. The ethoxylated sulfonates can be prepared by sulfonating ethoxylated alcohols. Sulfonated alcohols are excellent foamers as are the sulfonated versions of non-ionic surfactants. The ethoxylated sulfonates are also known as alcohol ether sulfonates. The laboratory results and field tests indicate that the mixed surfactant formulation composed of a petroleum sulfonate and ethoxylated sulfonate or alcohol can improve oil recovery as well as increase salinity tolerance. Ethoxylated sulfonates also lead to a greater flexibility in fluid system design because the degree of ethoxylation and/or the chain length may be varied to adjust slug viscosity. 

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