(465e) Wettability Alteration of Carbonates By Mixed Anionic and Non-Ionic Surfactants

Soumik Das¹, Quoc Nguyen² and Roger T. Bonnecaze^[1]*

¹ McKetta Department of Chemical Engineering, The University of Texas at Austin, Austin, TX, 78712

²Hildebrand Department of Petroleum and Geosystems Engineering, The University of Texas at Austin, Austin, TX, 78712

Only about 35% of oil in place is recovered from carbonate reservoirs through primary and secondary flooding because of oil wet surfaces and resulting unfavorable capillary pressures. Surfactants can improve oil recovery in such cases significantly by altering wettability of surfaces. In a previous study nonionic surfactants with different hydrophobic groups and different lengths of hydrophilic ethylene oxide oligomers have been found to be effective in altering the wettability of initial oil-wet carbonate surfaces¹. These surfactants, however, could only be used for reservoirs at a modest temperature as they precipitate at higher temperatures above its cloud point. In this study we examine formulations of anionic surfactants as co-surfactants to elevate the cloud point of non-ionic surfactants, for use in reservoir conditions of high temperature and salinity. The cloud points of such systems are significantly increased and the role of structure of the anionic co-surfactant on aqueous stability is discussed. We then present systematic study of the change in oil-water contact angle for combinations of different anionic and non-ionic surfactants. The extent of this wettability alteration is found to correlate with the difference between cloud point and temperature of the system. However, the nature of this correlation is found to depend on the structure of the co-surfactant. We also report the adsorption behavior of these mixed surfactant systems on carbonate surface and correlate the findings to cloud point and wettability alteration measurements. A simple thermodynamic model is then used to explain the behavior of aqueous stabilization and adsorption in such systems. Using the model along with experimental results, we predict surfactant systems which are viable for wettability alteration in high temperature and high salinity oil-wet carbonate reservoirs.

[1] Das, S., Nguyen, Q., Patil, P. D., Yu, W., & Bonnecaze, R. T. (2018). Wettability alteration of calcite by nonionic surfactants. Langmuir, 34(36), 10650-10658.

* rtb@che.utexas.edu