| dc.description.abstract | Previous experimental studies and limited field results have shown that the application of surfactants can be effective in improving recovery from unconventional liquid-rich reservoirs. Most of these studies and field applications have been conducted at temperatures below 200℉. The application of surfactants for EOR has not been evaluated at higher temperature conditions. However, many of the potential EOR candidates in the lower 48 are reservoirs that have temperatures greater than 200℉. For instance, temperatures greater than 320℉ in the Eagle Ford liquid-rich window have been reported. Therefore, this study aims to design surfactant systems that are thermally stable and effective for high-temperature EOR applications in shale reservoirs.
This study provides a complete workflow for surfactant selection for high-temperature EOR applications and presents guidelines for designing surfactant systems for these high-temperature conditions. Single ionic surfactant systems, as well as novel blends of ionic surfactants, were evaluated. The behavior of the different ionic surfactant systems was investigated through contact angle (CA) and interfacial tension (IFT) measurements for a wide range of temperatures up to 350℉ and pressures of up to 5000 psia. These measurements were performed with crude oil and oil-saturated rock samples obtained from a high-temperature Eagle Ford reservoir. Surfactant systems that were effective in altering wettability favorably at high-temperature conditions were further evaluated by Surfactant Assisted Spontaneous Imbibition in order to quantify their impact on improving oil recovery. Surfactant aqueous stability, time stability, and solubility were also investigated.
CA and IFT measurements reveal that temperature has a significant impact on the effectiveness of surfactant systems. At low-temperature conditions, some ionic surfactants were effective in altering wettability favorably. However, at increased temperatures, ionic surfactants showed limitations in altering the wettability favorably above a certain temperature limit tagged the ionic surfactant temperature limit (ITL). To ensure the applicability of surfactants at high-temperature, the ITL has to be above the reservoir temperature. Means of improving the ITL, as well as designing surfactants with higher ITL, became the paramount objective. Furthermore, it was revealed that the use of higher surfactant concentration and higher salinity systems improved the ITL, thereby making surfactant systems more effective for high-temperature applications. Optimal surfactant molecular structures to improve the ITL of the surfactant system are described. Novel co-surfactants systems, which are blends of cationic and zwitterionic surfactant systems, showed the most promising results for high-temperature applications with recovery factors up to 22.6% OOIP.
This study establishes a foundation in understanding the behavior of surfactant molecules at high-temperature conditions and unlocks the potential for improving oil recovery significantly in high-temperature unconventional reservoirs. | |
