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In this article, a novel salt-resistant pH-sensitive surfactant N-carboxystearamido methanesulfonic acid (MSA) was designed and synthesized. The rheological properties of the MSA/CTAB mixed system prepared using seawater were evaluated, and the variation laws of the related rheological parameters were discussed. The relevant fracturing technical parameters of the MSA/CTAB mixed system were comprehensively evaluated. The wormlike micelles formed by the non-covalent binding of MSA and CTAB molecules can resist the electrostatic effect of inorganic salts in the seawater. Meanwhile, the MSA/CTAB mixed system has an excellent pH response and revealed that the change from wormlike micelles to spherical micelles leads to the decrease of the apparent viscosity and the transition from Maxwell fluid to Newton-type fluid. Furthermore, the MSA/CTAB mixed system has excellent cyclic fracturing performance, which can meet the dual requirements of fracturing fluid cost and performance of offshore oilfield, and has a good application prospect.

The structure-activity relationship between the molecular structure of Gemini surfactants and foam properties has not yet been deeply revealed. In this study, we clarified for the first time the structure-activity relationship between foam properties and molecular structure of Gemini surfactant by discussing the variation characteristics of parameters such as free energy of interface formation, radial distribution function, and mean square displacement calculated by molecular simulation method. The research results show that (1) the Gemini surfactant with the sulfonic acid head group has the most excellent foam properties; (2) the foam properties increase monotonously with the increase of the hydrophobic tail chain length; (3) the foam properties decrease monotonously with the increase of the spacer group length. It is hoped that this article can further broaden the application range of surfactants as foaming agents in industrial fields such as oil and gas exploitation.