Investigation on Rheological Characterization and Salt Tolerance Potential of Paraffinic O/W Emulsions of Natural Surfactant for Crude Emulsification and Mobilization

While the presence of long-chain paraffinic compounds in crude oil seriously impacts oil production, they tend to form emulsions during flow through restricted pores. In turn, these emulsions help mobilize additional oil due to pore throat plugging, reducing interfacial tension, altering the wettability, and facilitating flow redistribution. The inclusion of a surfactant, especially of a natural biodegradable origin, can not only help promote emulsion formation to boost oil recovery but also lower the chemical footprint of the oil recovery process, making the entire process more sustainable. Therefore, in this study, a natural surfactant obtained from Fenugreek seeds has been explored to produce oil-in-water emulsions in conjunction with oil phases: n-pentane (EP1), n-hexane (EP2), n-heptane (EP3), and n-dodecane (EP4). Using visual observation and interfacial tension measurements over a range of 0.05–0.3 wt %, the optimum emulsifying surfactant concentration was identified to be 0.2 wt %. The emulsions were observed to be creamed by separating the aqueous phase over a span of 10 days, which was observed under a microscope. All emulsions tend to exhibit a shear thinning profile at ambient conditions, and the best fit was observed with Power Law with R2 values of 0.93, 0.91, 0.94, and 0.97 for solutions EP1, EP2, EP3, and EP4, respectively. Furthermore, the effect of monovalent (NaCl) and divalent (CaCl2) salts was explored, with EP4 found to be comparatively more stable than other emulsions. To understand the effect of heterogeneity of reservoirs, contact angle measurements were performed on sand base prepared with different sizes and pore size was found to be a critical factor influencing wettability alteration. Finally, the potential of natural surfactant in displacing the oil was visualized using a microfluidic setup wherein the injected surfactant solution was able to mobilize oil, paving a potential pathway for future field implementation for enhanced oil recovery operations.