Evaluation of oil-in-water microemulsion base ethoxylated surfactant under acid conditions

•Acid did not significantly change the microemulsion droplet size.•The rheological behavior of microemulsions studied were Newtonian.•The acid-carbonate wettability is enhanced in microemulsion media. This work investigates the stability of oil-in-water microemulsions prepared with nonionic surfactants under acid conditions and their interaction with a carbonate formation. The microemulsions were prepared with different acid concentrations. Measures of droplet size diameter, rheology, and surface tensions were performed. To evaluate the dynamic spreading behavior of the acid microemulsion on the carbonate rock surface, the contact angle of the acid systems was measured in time. Our results demonstrate that presence of the acid increases the stability of the microemulsion systems studied. We also observed that the rheological behavior is Newtonian, and the acid concentration affects only the viscosity. Our findings also indicate that microemulsions alter the pattern of spreading of the acid systems on the carbonate rock surface, rendering the outer acid solution more wettable to the carbonate rock. Thus, this study contributes to a better understanding of microemulsion formulated with nonionic surfactants, under acid conditions, and how they interact with the carbonate rock.