Smart water and low-salinity waterflooding showed encouraging results in carbonate and sandstone reservoirs, respectively, at lab and field scales. Adjusting the injection water salinity and/or composition in either secondary or tertiary mode can positively instigate chemical interactions between reservoir fluids and rock minerals for enhanced oil recovery,. Several macroscopic and traditional laboratory techniques including coreflooding, contact angle, surface charges, NMR, and IFT have been extensively used to understand reaction mechanisms and subsequently optimize the water flooding process.

It is quite challenging to understand the behavior of reservoir fluids and water ions with carbonate minerals at very fine microscopic levels. Advanced technologies are required to comprehend the in-situ interactions at dynamic and static conditions. Cryogenic high resolution transmission electron microscopy (Cryogenic-HRTEM) equipped with energy dispersive spectroscopy (EDS) are utilized in this study to image oil droplets and dissolved salt ions at their native environment. Furthermore, Super-X EDS system? is used simultaneously to image the compositional distribution of multiple elements and to provide elemental mapping of the structures in solution. The experiments have been conducted using two different methodologies involving cryogenic-SEM and cryogenic-TEM. In addition, different fluids as crude oil, seawater and smartwater are observed at interfaces.

Results from this study revealed for the first time the in-situ distribution of mono and divalent ions around crude oil droplets. The elemental maps were shown to be distinct across the fluids and oil droplet interfaces. In comparison to seawater, smartwater reacted differently with crude oil components, and as a result, the interfacial layer thickness determined to be approximately 20 angstroms. This study gives a new insight about the elements’ distribution and interfacial layer's characteristics at different oi/brine interfaces. In summary, the observation at interfaces especially with smart water can alter the carbonate rock wettability towards water-wet for better oil recovery.

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