CHEMICAL-STABILITY OF ETHOXYLATED SULFONATE OLIGOMERS RELATED TO IMPROVED OIL-RECOVERY

A commercial product of nonylphenyl ethoxylated sulfonate, C9-Ph-(EO)6-SO3Na, which is strongly polydisperse in the EO number, has been tested for chemical stability in relation to improved oil recovery conditions. The surfactant mixture was dissolved in synthetic sea water containing a variety of additives, i.e. oil, kaolinite, quartz, transition metals, and reservoir rock, and stored at 80-degrees-C under both aerobic and anaerobic conditions. The objective of the test was to study if any selective degradation of the various x(EO)-sulfonate oligomers (2 < x < 14) took place during an incubation period of 150 days. No change in the x(EO)-sulfonate distribution was observed in the case of the oil-free samples. For the oil-containing samples the x(EO)-sulfonate distribution of the material dissolved in the water phase showed an enrichment of the lower x(EO)-number oligomers. This is suggested to be caused by a phase transition of the longer x(EO)-sulfonate oligomers into an emulsion which was formed during the test period.