Add time:08/14/2019         Source:sciencedirect.com

Clay-rich sandstone formations contain vast deposits of petroleum resources. Low salinity waterflooding presents a low-energy, low-environmental impact method to improve oil recovery from these systems. Fundamental mechanisms dictating improved oil recovery at low salinity conditions are not well-understood currently. This study investigates low salinity waterflooding at the pore-level to delineate fundamental mechanisms underlying oil recovery. Clay-functionalized, two-dimensional micromodels are used to provide direct visual observations of crude oil, brine, and clay particle interactions within the pore-space. Using this microvisual approach, establishment of initial reservoir conditions shows wettability evolution of the initially water-wet system towards a mixed-wet condition due to clay-particle interactions with the reservoir fluids, i.e., crude oil and brine. Pore-scale behavior during low salinity waterflooding shows spontaneous emulsification of the crude oil and brine. Specifically, the emulsions generated are Pickering type stabilized by the clay particles that were mobilized at salinities below the critical salt concentration (CSC). Spontaneous generation of the stable Pickering emulsions reduces mobility through preferential flow paths, thereby resulting in flow diversion of subsequent injection fluids to mobilize oil-filled pores. Leveraging the stability of the Pickering emulsions, a sequential salinity cycling method is developed to improve overall oil recovery by an additional 8% of the original oil in place. Flow diversion due to spontaneous Pickering emulsification in preferential flow paths observed here provides fundamental insight to the design and application of low energy-input, low environmental-impacts techniques in the field.

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