Synthesis of betaine surfactant and its application in microemulsion flushing fluid

Abstract

In order to effectively remove the oil-based drilling fluid and oil mud cake attached to the wellbore, improve the cementation environment of the second interface and improve the quality of cementing, a betaine-type zwitterionic surfactant (OASB) was synthesized in this study. The structure of OASB was characterized by IR and ¹H NMR. The interfacial tension of OASB solution with different concentration was measured. A microemulsion cementing flushing fluid (MFF) was prepared with OASB mixed with Tween 80 as surfactant, n-octanol as cosurfactant, kerosene as oil phase and deionized water as water phase. The stability, particle size, rheology, corrosivity and wettability of MFF were analyzed and tested. The flushing effect of MFF on oil-based drilling fluid and oil mud cake was evaluated, and the changes in bonding strength of the second interface of cementing before and after flushing was compared and analyzed. The results revealed that MFF had good temperature, salt, acid and alkali resistance and low corrosion ability. The apparent viscosity was 25 ∼ 80 mPa·s in 20 ∼ 120 °C and had good rheological properties. The excellent wettability reversal ability of MFF was beneficial for removing oil-based drilling fluid and oil mud cake, with a flushing efficiency of over 90%. After MFF flushing, the bonding strength of the second interface of cementing was significantly improved. The SEM and elemental analysis showed that MFF had a more thorough flushing of oil mud cake, and the bonding structure between the cement stone and the second interface was denser.

Graphical Abstract

Keywords:

• Surfactant
• microemulsion
• flushing fluid
• oil-based drilling fluid
• bonding strength of the interface

Acknowledgements

The authors are very grateful to the research group of oil and gas well cementing functional materials of Southwest Petroleum University for their suggestions and help in this research work. The authors also thank the State Key Laboratory of Oil and Gas Reservoir Geology and Development Engineering of Southwest Petroleum University for providing equipment support.

Disclosure statement

The authors declared that they have no conflicts of interest to this work. We declare that we do not have any commercial or associative interest that represents a conflict of interest in connection with the work submitted.