Novel Characterization of Thin Film at Reservoir Fluids Interfaces in Carbonates

The salinity and ionic strength of injection water can make favorable impacts on wettability and oil recovery in different carbonate and sandstone reservoirs. The interaction mechanism between dissolved ions in injection water and reservoir fluids is a key ongoing research area. Most of these interactions occur at the thin film interfaces and so are considered one of the challenges in identifying and understanding the mechanisms. Conventional macro and microscopic laboratory techniques are commonly applied to determine contact angles, surface charges, and coreflooding to measure any incremental increase in oil recovery. In this paper, advanced sum frequency generation (SFG) spectroscopy is utilized, for the first time, to characterize the chemical structures of molecules at the brine/crude oil interfaces. The change in the chemical structure is perceived with time at a broad wavenumber range from 1000 to 3900 cm−1. Distinct spectral signatures of oil components and water ions are detected for high salinity water (HSW), modified ionic strength water (MIW), and ions-free solutions. The SFG data is also compared with the previous macroscopic wettability results to predict the components that are highly affected during waterflooding/enhanced oil recovery (EOR) processes. This study brings new insights about understanding the chemical structures at brine/crude oil monolayers and aqueous interfaces. The measured spectra at the interfaces along with the observed signal intensity trends are discussed in terms of composition and structure of organic and inorganic components. For example, SFG results from MIW oil interfaces and has higher spectral intensity at 2860 and 1700 cm−1 wavenumbers when compared with other brines used. These results exactly correlate with the C-H and C=O stretching bonds, which consider the key oil components at the interfaces. The novelty of this interfacial study can give more ability to understand the reaction mechanisms as altering the ionic strength and salinity of the injection water. Such understanding is also crucial in optimizing the chemistry of injection water and its interaction with oil components and carbonate rock to ultimately alter wettability toward water-wet.