Smart water and low-salinity waterflooding showed encouraging results for oil recovery in carbonate and sandstone reservoirs. Therefore, understanding of multiphase flow phenomena in reservoir rocks is critical to optimize injected water formulations and increase oil recovery. Various micro- and macroscopic techniques including NMR, surface charges, IFT, contact angle and coreflooding have been extensively used to understand the underlying mechanisms responsible for rock wettability alteration. However, it is challenging to understand the behavior of reservoir fluids and carbonate rocks at nano-scale with conventional methods, hence there is a need for advanced technologies to identify fluid phases and distributions at pore scale. The primary objective of this study is to develop an experimental protocol using Cryogenic high resolution focused ion beam (Cryo-FIB SEM) equipped with energy dispersive spectroscopy (EDS) and apply the developed protocol to study the impact of ions on carbonate rock/crude oil/brine interface at nano-scale. Cryo FIB-SEM preparation and imaging provide pore structure, connectivity and fluids distribution at carbonate pore scale. While, EDX analysis gives an insight of the compositional distribution and elements mapping. For carbonates exposed to calcium chlorides, SEM analysis showed the presence of hydrocarbons with a newly formed phase inside the pores, indicating the presence of high concentration of oxygen bonds. While no newly formed phase was observed for carbonate rock exposed to a complex brine. EDS analysis have also provided an elemental mapping based on the composition of the brine used. This feasibility study showed that the experimental protocol permits the observation of carbonate porosity morphology, fluids distributions inside the pore and elemental mapping across the surface for a better understanding of the crude oil/brine/carbonate system.

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