Interfacial Tension and Wettability Change Phenomena during Alkali-Surfactant Interactions with Acidic Heavy Crude Oil

In this work, a newly formulated sulfonate-based surfactant and two other commercial sulfate-based surfactants with the capability of tolerating harsh underground reservoir conditions, such as high-saline formation water and high temperature, were prepared. Sodium metaborate as an effective alkali compound was also used to provide alkalisurfactant combination. Interfacial tension (IFT) measurements as well as wettability examinations for different salinities and mixture conditions were performed for an extended range of the chemical concentrations. The wettability tests including both contact angle measurements and Amott cell tests were performed on saturated Berea sandstone plug samples and rock slices, while the precise spinning drop technique was used for IFT measurements. The mixtures of both surfactant groups and alkali resulted in a minimum IFT value required to attain an optimum three-phase region at high-salinity conditions. The addition of the alkali to the surfactant solution reduced the lowest IFT value to less than 0.005 mN/m in the solutions containing 0.5 wt % alkali and 0.2 wt % of each surfactant. The synergistic effect of the surfactants and in-situ-generated soap as the result of the injected alkali reaction with the carboxylic compounds of the crude oil provided promising results for microemulsion generation in the solution; however, with special composition of the sulfonate-based surfactant, the acquired optimum solution salinity was reduced. Although both contact angle and Amott cell tests were performed to assess the wettability changes, the results indicated that the contact angle technique was not reliable enough when the solution contains highly reactive materials. Both of the surfactant groups were able to reduce the oil-wetness of the core plugs; however, mixtures of the sulfonate-based surfactant and sodium metaborate improved the spontaneous oil recovery efficiency from core plugs during imbibition and drainage processes.