Thermal Stability of Surfactants for Reservoir Application

Abstract

AbstractThe thermal stabilities of several sulfonate surfactants and one nonionic surfactant have been evaluated. The decomposition reactions have been observed to follow first-order kinetics. Consequently, a quantitative measure of a surfactant's stability at a given temperature is its half-life. Furthermore, the activation energy can be estimated from rate data obtained at two or more temperatures. This permits limited extrapolation of the observed decomposition rates to lower temperatures for which the rates are too low for convenient measurement. The surfactants we investigated are being considered for steamflood additives and need to be relatively stable at steam temperatures.None of the surfactants evaluated to date has the requisite stability for use in steamfloods. The most stable petroleum sulfonate we have investigated has a half-life of 11 days at 180°C (356°F). With this half-life, substantial overdosing would be required to maintain the minimum effective surfactant concentration for the life of the flood. On the other hand, the estimated half-life for this surfactant at 93°C (200°F), calculated by extrapolation, would be 33 years.Tests with the nonionic surfactant, nonylphenoxy-polyethanol, have shown this material to have a very short half-life at steam temperatures, but it does appear to be more stable at concentrations greater than the critical micelle concentration (CMC). In limited tests, the sulfonates showed increased stability in the presence of a 2-M salt solution.