A fast and accurate method,based on multipoint electrical measurements,is used to monitor the hydrocarbon mobilization/dissolution in a porous medium,during the ratecontrolled injection of a surfactant solution.The residual n-C_(10) remaining in a soil column after a fast drainage and a slow imbibition step is flushed by an aqueous solution of NaCl(17.5 g/L) and anionic surfactant SDS(4.9 g/L).The transient response of the water saturation averaged over five successive segments of the soil column is monitored by transforming the electrical resistance between five pairs of electrodes to water saturations with the aid of a non-Archie equation.The sequential mobilization and entrapment of n-C_(10) ganglia in the various segments are fast processes observed during the first stages of the flushing test,while the n-C_(10) dissolution in aqueous and SDS micelle phases is a slow process observed mainly during advanced stages of the test.A mathematical model of surfactant enhanced hydrocarbon dissolution and mobilization is developed.Based on the experimental data,an effective dissolution rate(EDR) is determined explicitly over each soil column segment.The EDR is the sum of the actual n-C_(10) dissolution rate and the net rate of n-C_(10) mass outflow through the soil segment.
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