摘要

There has been no fundamental work in the literature accentuating microscale behavior of different present phases in an oil reservoir and injected aqueous surfactant solutions and their mutual interactions both in the presence and absence of connate water saturation in dilute surfactant flooding. In this work, a glass micromodel was used to provide new insight into the fundamental issues associated with microscale interactions of oil and aqueous surfactant solutions with connate water. Surfactant flooding tests were conducted both in the presence and absence of connate water to better highlight the influence of connate water on microscopic phenomena as well as macroscopic behavior and performance of the surfactant flooding. This fundamental study revealed that the presence of connate water can decrease the active or working surfactant concentration and significantly modify the local and global microscopic displacement efficiencies, oil recovery efficiencies, and dominancy of the promoted surfactant solution imbibition in determining the oil recovery efficiency. The presence of connate water can also affect the extent of contribution of produced oil-in-surfactant solution emulsions to the improved oil recovery (especially after surfactant solution breakthrough) during the displacement of oil by aqueous surfactant solution in the porous medium. These phenomena occurred mainly due to the inalienable dilution of the surfactant solution by the connate water and possible promoted mass transfer between the mobilized connate water and surfactant solution, which could decrease the active or working surfactant concentration within the surfactant solution.