We propose a new systematic procedure to investigate the effect of hydrophobic and hydrophilic chain lengths of polyoxyethylenated (POE) nonionic surfactants on dynamic interfacial properties in porous media. We study the impact of nonionic surfactant structure on oil recovery through comprehensive experimental measurements of phase behavior, cloud point, dynamic interfacial tension, dynamic contact angle, and spontaneous and forced imbibitions at ambient and reservoir conditions. We identify a surfactant structure that increased the oil production by 22% and 6% compared to tap water and a nonionic surfactant commercially deployed in a major unconventional oil reservoir, respectively. In this work, we observe that factors such as minimum interfacial tension used for surfactant selection are not the only parameters influencing displacements at the pore scale. The results of this study reveal that when a surfactant solution imbibes into the pore space as an invading phase, the surfactant ability to lower the IFT and reach equilibrium faster plays an important role in the local trapping of oil phase on a pore-by-pore basis. We propose a mechanism relating this surfactant behavior to oil−brine displacement and confirm our results by visual observation of in situ pore fluid occupancies after surfactant imbibition in micromodels and naturally occurring porous media.
Capillary trapping is a physical mechanism by which carbon dioxide (CO 2 ) is naturally immobilized in the pore spaces of aquifer rocks during geologic carbon sequestration operations, and thus a key aspect of estimating geologic storage potential. Here, we studied capillary trapping of supercritical carbon dioxide (scCO 2 ), and the effect of initial scCO 2 saturation and flow rate on the storage/trapping potential of Berea sandstone. We performed two-phase, scCO 2 -brine displacements in two samples, each subject to four sequential drainage-imbibition coreflooding cycles to quantify end-point saturations of scCO 2 with the aid of micro-and macro-computed tomography imaging. From these experiments, we found that between 51% and 75% of the initial CO 2 injected can be left behind after the brine injection. We also observed that the initial scCO 2 saturation influenced the residual scCO 2 saturation to a greater extent than the rate of brine injection under the experimental conditions examined. In spite of differences in the experimental conditions tested, as well as those reported in the literature, initial and residual saturations were found to follow a consistent relationship.
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