Synthetic chemical surfactants deployed in the petroleum industry to improve oil recovery to meet growing global energy demand are described to have detrimental environmental impacts and are expensive. In recent times, the exploration of saponin-rich plants as a substitute for environmentally threatening synthetic surfactants has garnered significant interest from researchers. Saponin-based natural surfactants (SBNSs) are nontoxic, biodegradable, and possess desirable properties for use in the oil and gas industry. This paper reviews the potential application of saponin-based natural surfactants in enhanced oil recovery processes that coincide with the interests of the United Nations' Sustainable Development Goal 7 for Affordable and Clean Energy. We reviewed the mechanisms of saponin-based natural surfactants in enhanced oil recovery (EOR), surfactant adsorption, and the recent advances in utilizing saponin-based natural surfactants for EOR purposes. We also provided a comprehensive analysis of the impact of salinity and temperature on the performance of SBNSs. Moreover, the study also presented the economic feasibility and limitations of SBNSs for field enhanced oil recovery applications. We identified that a good number of SBNSs can withstand harsh reservoir conditions, optimize interfacial tension by as high as 95.82% (although not to ultralow levels), and alter rock wettability from hydrophobicity to hydrophilicity, thereby reducing the contact angle by 3.64% to 87.5%. SBNSs also successfully yielded a high incremental oil recovery factor of up to 36% in the postsecondary recovery stage. The advent of techniques, such as alkali incorporation and nanotechnology, support the achievement of ultralow interfacial tension, mitigation of surfactant adsorption, and oil recovery improvement. Future studies can adopt the recommendations outlined in this study to minimize uncertainty in the utilization of SBNSs and enhance their design for "green" chemical enhanced oil recovery applications.
A viable CO2 storage resource must have sufficient storage capacity, reliable containment efficiency and adequate well injectivity. Deep saline formations stand out in terms of storage capacity and containment efficiency. However, formation brine dry-out and salt precipitation in the near well region could impair CO2 injectivity in deep saline reservoirs, thus reducing their potential for CO2 storage. Core-flood experiments and analytical modelling were used to investigate various mechanisms of external and internal salt precipitation. Particularly, the impact of the extension of the dry-out region on CO2 injectivity was investigated. It was found that, for high permeability rocks, injection of CO2 at relatively low injection rates could result in salt cake deposition at the injection inlet especially under high salinity conditions. It was also found that extension of the dry-out region does not have significant impact on CO2 injectivity. Although the magnitude of CO2 injectivity impairment increased more than two-fold when initial brine salinity was doubled, real-time changes in CO2 injectivity during the drying process was found to be independent of initial brine salinity. We have shown that the bundle-of-tubes model could provide useful insight into the process of brine vaporization and salt deposition in the dry-out region during CO2 injection. This work provides vital understanding of the effect of salt precipitation on CO2 injectivity.
A viable CO2 storage resource must have sufficient storage capacity, reliable containment efficiency and adequate well injectivity. Deep saline formations stand out in terms of storage capacity and containment efficiency. However, formation brine dry-out and salt precipitation in the near well region could impair CO2 injectivity in deep saline reservoirs, thus reducing their potential for CO2 storage. Core-flood experiments and analytical modelling were used to investigate various mechanisms of external and internal salt precipitation. Particularly, the impact of the extension of the dry-out region on CO2 injectivity was investigated. It was found that, for high permeability rocks, injection of CO2 at relatively low injection rates could result in salt cake deposition at the injection inlet especially under high salinity conditions. It was also found that extension of the dry-out region does not have significant impact on CO2 injectivity. Although the magnitude of CO2 injectivity impairment increased more than two-fold when initial brine salinity doubled, the development of CO2 injectivity was found to be independent of initial brine salinity. We have shown that the bundle-of-tubes model could provide useful insight into the process of brine vaporization and salt deposition in the dry-out region during CO2 injection. This work provides vital understanding of the effect of salt precipitation on CO2 injectivity.
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