Effect of Temperature on Surfactant Adsorption in Porous Media
Abstract The effect of temperature on the adsorption of asulfonate surfactant and a nonionic surfactant ontocrushed Berea sandstone was studied by both staticand dynamic techniques. Static experiments were conducted over atemperature range from 25 to 95 degrees C to definetemperature-sensitive rock/surfactant systems and toestablish the shape of the equilibrium isotherm.Dynamic experiments served to reinforce the findingsof the static tests and extended the temperature rangefor sorption to 80 degrees C. This is a typicalsteamflood temperature. A mathematical model thatincorporates the mass transport, thermal degradation, and rate-dependent adsorption of the surfactantrepresented these dynamic results. The model wasused to determine the effect of temperature on the sorption rate constants. Mineral dissolution at elevated temperatures hasbeen found to cause precipitation of the sulfonate.Adsorption of the nonionic surfactant decreased withan increase in temperature at low concentrations, whereas the opposite was true at high concentrations.This has favorable implications for a low-concentration injection scheme. When performingstatic adsorption experiments, care had to be takenbecause of the poor thermal stability of the nonionic surfactant. Introduction Injection of surfactants concurrently with steam intooil-bearing reservoirs has been proposed recentlyto improve the recovery efficiency of the steam-driveprocess. From the behavior of chemical additivespreviously used in steamfloods, it is anticipated thatthe injected surfactant will travel through thatportion of the reservoir being flooded by hot water. Oil recovery can be increased if the surfactanteffectively reduces the residual oil saturation withinthis hot-water zone. For concurrent surfactant/steam injection to be technically attractive, a synergisticeffect between the surfactant and temperature isdesired. In our concept of the process, the surfactant mustmove in the heated portion of the reservoir and beable to function as an effective recovery agent atelevated temperatures for prolonged periods of time.Surfactant screening, therefore, requires thisinformation:surfactant stability under steamfloodconditions,temperature effects on the interfacial tension (IFT) between the reservoir oil and aqueoussurfactant,an evaluation of the effect oftemperature on surfactant flood performance, andthe effect of temperature on surfactant adsorption atthe water/solid interface. Handy et al. reported the thermal stabilities ofseveral classes of surfactants. Hill et al. showed thattemperature can have a dramatic effect in reducingthe IFT between crude oil and an aqueous sulfonatesystem. Handy et al. saw a similar temperatureeffect for a nonionic-surfactant/crude-oil system. Itappears, therefore, that the required synergismbetween temperature and surface activity necessaryfor concurrent surfactant/steam injection exists.Surfactant core floods are required to evaluate theeffect of temperature on oil recovery. Finally, toensure that the surfactant moves in the heatedportion of the reservoir, it is necessary to determinethe effect of temperature on adsorption. SPEJ P. 218^