Preparation of a salt-responsive Gemini viscoelastic surfactant for application to solids-free drilling fluids

In order to solve the problem of poor rheological properties of solid-free drilling fluids in salt-bearing formations and prevent drilling accidents such as lost circulation, formation collapse, and wellbore instability, it is crucial to develop a new type of viscosifier. In this study, a salt-responsive Gemini viscoelastic surfactant (NT-1) was synthesized by using erucamide as a hydrophobic chain and introducing a benzene ring and a carboxyl group into the linker. In addition, it is used as a viscosifier for solid-free drilling fluids. The structure of the surfactant was characterized by H-1 nuclear magnetic resonance (NMR), C-13 NMK, Fourier transform infrared spectroscopy, and electrospray ionization tandem mass spectrometry (ESI-MS), and its physicochemical properties were determined by surface tensiometer, thermogravimetric-differential scanning calorimetry, dynamic lighting scattering and rheometer. Its performance in solid-free drilling fluids was evaluated according to the American Petroleum Institute (API) standard. The results show that the surfactant has a low critical micelle concentration (31.74 mol/L), excellent thermal stability and water solubility. In particular, NT-1 can self-assemble into worm-like micelles under the action of salt, and the spatial network structure formed by the interweaving of these micelles can endow the drilling fluid with good rheology and viscoelasticity. NT-1 is compatible with conventional drilling fluid polymer additives, which can effectively improve solid-free drilling fluids rheological properties and fluid loss properties in salt layers. The temperature resistance in drilling fluid systems can reach 120 degrees C. This work verifies the feasibility of using viscoelastic surfactants as viscosifiers in solid-free drilling fluids and provides new ideas for developing salt-responsive smart drilling fluids.