Pore-Scale Imaging of Emulsification of Oil during Tertiary and Secondary Low Salinity Waterflooding in a Reservoir Carbonate

While it is known that changing the salinity of the brine used to displace oil in porous rock can lead to additional recovery, the mechanism by which this occurs at the pore scale is still not fully understood. We investigate whether the emulsification of oil is the process by which recovery is improved, removing oil from the solid surface and rendering the rock more water-wet. High-resolution three-dimensional X-ray imaging was used to visualize the emulsification kinetics during secondary and tertiary low salinity waterflooding in a carbonate reservoir rock. The rock samples were imaged during water flooding, where the salinity of the injected brine was much lower than that of the formation water. An intermediate phase that appeared to be a mixture of oil and brine, and which we hypothesize is an emulsion, was imaged in both tertiary and secondary low salinity waterflooding experiments. The formation of this intermediate phase is observed to be the preliminary step prior to oil mobilization. Gray-level histograms and pore occupancy maps showed a faster displacement of oil in the secondary mode compared to tertiary flooding where the emulsified oil remained in the sample for longer before displacement.