The Synergic Effect of Brine Salinity and Dispersed Clay Particles on Water-in-Heavy Oil Emulsion: Insight into Asphaltene Structure and Emulsion Stability

Summary The research on enhancing oil recovery in sandstone reservoirs through low-salinity waterflooding (LSWF) has been well-documented, while there have been few studies conducted on the impact of emulsion formation in heavy oil due to the incompatibility between the injected brine, clay particles, and heavy oil components. In this study, we explored the synergic role of asphaltene and clay in the process of LSWF by introducing an innovative and thorough experimental approach. Our findings presented new insights into how LSWF in clay-rich sandstone reservoirs can influence the behavior and properties of the water-in-heavy oil emulsions. In this regard, we contacted the heavy oil and brine (with and without clay) for 20 days at 90°C. Then, the emulsion was centrifuged to separate the oil and brine phases. The oil phase was examined by conducting the viscosity, interfacial tension (IFT), Fourier transform infrared spectroscopy (FTIR), and asphaltene onset point (AOP) precipitation experiments. Significant decreases in viscosity and asphaltene precipitation values were observed when crude oil was exposed to clay solutions, as indicated by viscosity and IP-143 results. Furthermore, the zeta potential of clay particles suspended in various brines was determined to assess the electrostatic aspects of rock-oil interactions. The analysis of the emulsion phase indicated that the emulsion stability in the presence of clay increased because of the improvement of asphaltene contribution in the interface. This trend aligns with the zeta potential measurement results. In addition, after examining the pH and conductivity of aged brine in the presence and absence of clay, it was observed that the clay caused the release of hydrogen ions in the brine and then bonded with the dissolved cations, leading to improvement in the emulsion stability. Ultimately, the asphaltene molecular structure was compared via scanning electron microscopy (SEM) and attenuated total reflection analysis before contact with the brine and after separation from the emulsion phase. The results indicated a decrease in the concentration of aliphatic groups in the molecular structure of the remaining asphaltene following the aging of the oil bulk. These new findings can potentially mitigate unwanted emulsion damage in the LSWF in heavy oil recovery. Additional Keywords emulsion; asphaltene; low-salinity waterflooding; clay; heavy oil; zeta potential