Mechanism and Influencing Factors of Wettability Alteration of Water-Wet Sandstone Surface by CTAB

Abstract

Different experimental methods including ellipsometry, zeta potential measurements, imbibition studies, and contact angle measurements were used to study the mechanism and influencing factors of wettability alteration of water-wet sandstone surface caused by CTAB (hexadecyl trimethyl ammonium bromide). Results show that when the concentration of CTAB reaches a certain level (below CMC), due to the electrostatic attraction between the positively charged head groups of CTAB and the negatively charged sandstone surface, the monolayer of CTAB is formed and hydrophobic chains of CTAB molecules are toward the aqueous phase, making the solid surface oil-wet. When the concentration of CTAB continues to increase (above CMC), due to the hydrophobic interaction, the compact bilayer of CTAB is formed and hydrophilic head groups of CTAB molecules are toward the aqueous phase, rendering the solid surface water-wet. The contact angles between the oil–water interface and the surface treated with CTAB increase with the increase of the concentration of NaCl and CaCl_2. Compared to NaCl, the inorganic salt CaCl₂ has a greater impact on the contact angle. In addition, the contact angles increase with the increase of temperature and decrease with the increase of pH value of the aqueous solution.

GRAPHICAL ABSTRACT

Keywords:

• CTAB
• influencing factors
• mechanism
• sandstone surface
• wettability alteration

ACKNOWLEDGMENTS

The authors are grateful to the Center for Bioengineering and Biotechnology of China University of Petroleum for the access of the Ellipsometer. We also thank Shi-xun Bai from College of Petroleum Engineering, China University of Petroleum (East China), for providing help in article language polishing.