Effect of propylene glycol substituted group on salt tolerance of a cationic viscoelastic surfactant and its application for brine-based clean fracturing fluid

Abstract

In this study, a cationic viscoelastic surfactant (VES) called N-erucamidopropyl-N, N-dimethyl-N-(1, 2)-propylene glycol ammonium chloride (EDPG) with an unsaturated erucyl amide (C25) tail and a propylene glycol group was developed, which has an ultra-high salt tolerance compared to that of UC22AMPM. As with the zwitterionic VES of EDAS, EDPG molecules can aggregate into wormlike micelles (WLMs) in high-salinity solutions (above 10 wt% NaCl concentration) to impart viscoelasticity to the solutions, and their production cost is comparatively low. The surface tensions of EDPG and EDAS were measured in deionized water and salinity solutions to study the surface activities and the packing parameters (P) as functions of salinity, and the results showed completely different mechanisms regarding the salt tolerances of EDPG and EDAS. The propylene glycol group imparts a larger initial equilibrium area per molecule on the aggregate surface (a0) of EDPG, which can keep the P between 1/3 and 1/2 under ultra-high-salinity conditions to ensure the presence of WLMs. However, the salt tolerance of EDAS is attributed to its insensitivity to salinity because it is a zwitterionic betaine VES. The aggregation behavior of EPDG, EDAS, and UC22AMPM and the viscoelastic properties and microstructures of the EDPG solutions as functions of salinity were investigated using DLS, NMR, cryo-SEM, and oscillatory measurements to further confirm the salt tolerance of EDPG. Additionally, brine-based clean fracturing fluids prepared using EDPG and simulated brines exhibited good performance that meets the requirements of hydraulic fracturing fluid, according to a series of laboratory evaluation.