| abstract |
Primary anionic surfactants such as organic sulfonates, specifically petroleum sulfonates as well as synthetic alkyl or alkylaryl sulfonates are effective for recovering oil from subterranean, oil-containing formations only if the salinity and/or concentration of divalent ions in the formation water is relatively low. Many petroleum formations contain water whose salinity is in excess of the tolerance level of organic sulfonates, and either the high salinity water must be displaced by a preflush or the primary anionic organic sulfonate surfactants must be used in conjunction with an effective solubilizing co-surfactant in order to increase the solubility of the organic sulfonate in the high salinity and/or hard water. Suitable solubilizing co-surfactants include ethoxylated alcohols, alkyl phenols, and alkyl or alkylaryl thiols, as well as sulfated or sulfonated, ethoxylated alcohols or alkyl phenols. Optimum performance in any particular field is achieved if the ratio of primary anionic surfactant to solubilizing co-surfactant is carefully chosen so the surfactant combination exhibits borderline solubility in the particular formation water in which the surfactants are to be employed. The concentration ratio of primary and solubilizing surfactants which results in the desired borderline solubility may be identified by preparing a number of samples in the formation water using different ratios of primary surfactant concentration to solubilizing co-surfactant concentration, measuring the electrical conductivity of the samples and choosing the concentration ratio corresponding to the sample which produced the minimum electrical conductivity, or at which point the conductivity vs. concentration ratio curve exhibited an inflection point. |