| dc.description.abstract | The focus of this study was the use of nonionic surfactants and novel nonionic-ionic surfactant blends for enhanced oil recovery in high-temperature liquid-rich unconventional reservoirs. Through cloud point, wettability, IFT, and spontaneous imbibition experiments, 23 industrial surfactants samples (individual and blends) were investigated in an effort to design surfactant systems which could withstand temperature and pressure conditions from atmospheric up to 350˚F and 5000 psi.
Although surfactants have proven successful and cost-effective in enhancing production from conventional and unconventional reservoirs, studies that used nonionic surfactants have been limited to reservoirs with temperatures below 200˚F due to the temperature-dependent physiochemical properties of these surfactants. Therefore, this study aims at designing surfactant blends for reservoirs like the Eagle Ford and Monterey formation in the US and the Embla field in Norway, whose reservoir temperature is above 300˚F. The effectiveness of the surfactants in reducing the interfacial tension (IFT) at the oil-brine boundary and restoring contact angle (CA) to water-wet (Ɵ < 75˚) were the critical factors in choosing the most appropriate systems.
Results showed that the amount of ionic cosurfactant used affected thermal stability, with increasing concentration leading to increasing cloud point temperature (CPT). Wettability alteration was seen to be dependent not only on temperature but on the class of ionic cosurfactant. Cationic cosurfactants were observed to be better at improving the thermal stability of the nonionic surfactant. However, they resulted in oil-wet contact angles with increasing temperature. On the other hand, anionic cosurfactants displayed better synergy in terms of wettability alteration, creating strongly water-wet and intermediate contact angles at high temperatures. Therefore, focus was placed on nonionic-anionic surfactant blends for the reservoir sample used in this study.
In the end, stable surfactant blends with cloud point temperatures from 316˚F to 348˚F were created for EOR applications in high-temperature conditions. Spontaneous imbibition studies using these blends indicated an improved recovery of up to 173%. Therefore, this work was successful in providing novel and cost-effective surfactant solutions for EOR in high-temperature conditions. This study ergo serves as a template for the surfactant screening and selection process to be undertaken when considering nonionic surfactants. And, valuable insight on the mechanisms of nonionic surfactant blends is provided to help in further design and application situations. The surfactant solutions designed for the reservoir under investigation produced tight emulsions, implying surface treatment will be required in some fields to deal with possible emulsions problems. | |
