There have been many reports about the thickening ability of nanoparticles on the wormlike micelles in the recent years. Through the addition of nanoparticles, the viscosity of wormlike micelles can be increased. There still exists a doubt: can viscosity be increased further by adding more nanoparticles? To answer this issue, in this work, the effects of silica nanoparticles and temperature on the nanoparticles-enhanced wormlike micellar system (NEWMS) were studied. The typical wormlike micelles (wormlike micelles) are prepared by 50 mM cetyltrimethyl ammonium bromide (CTAB) and 60 mM sodium salicylate (NaSal). The rheological results show the increase of viscoelasticity in NEWMS by adding nanoparticles, with the increase of zero-shear viscosity and relaxation time. However, with the further increase of nanoparticles, an interesting phenomenon appears. The zero-shear viscosity and relaxation time reach the maximum and begin to decrease. The results show a slight increasing trend for the contour length of wormlike micelles by adding nanoparticles, while no obvious effect on the entanglement and mesh size. In addition, with the increase of temperature, remarkable reduction of contour length and relaxation time can be observed from the calculation. NEWMS constantly retain better viscoelasticity compared with conventional wormlike micelles without silica nanoparticles. According to the Arrhenius equation, the activation energy E_a shows the same increase trend of NEWMS. Finally, a mechanism is proposed to explain this interesting phenomenon.

In order to broaden the application of clean fracturing fluid in ultra-high temperature reservoirs, a surfactant gel for high-temperature-resistant clean fracturing fluid was developed with a gemini cationic surfactant as the main agent in this work. As the fracturing fluid, the rheological property, temperature resistance, gel-breaking property, filtration property, shear recovery performance and core damage property of surfactant gel were systematically studied and evaluated. Results showed the viscosity of the system remained at 25.2 mPa·s for 60 min under a shear rate of 170 s⁻¹ at 200 °C. The observed core permeability damage rate was only 6.23%, indicating low formation damage after fracturing. Due to micelle self-assembly properties in surfactant gel, the fluid has remarkable shear self-repairability. The filtration and core damage experimental results meet the national industry standard for fracturing fluids. The gel system had simple formulation and excellent properties, which was expected to enrich the application of clean fracturing fluid in ultra-high temperature reservoirs.

Wormlike micelles provide the structural basis for the viscoelasticity of clean fracturing fluids, yet the molecular mechanism by which calcium-containing brine regulates their growth remains insufficiently understood. In this work, all-atom molecular dynamics simulations were performed to investigate the calcium-regulated self-assembly of an EAHSB/EHAC/NaPts surfactant–counterion system. In the absence of Ca²⁺, dispersed surfactant and counterion molecules first formed small spherical aggregates, which subsequently fused into larger micelles, rod-like intermediates, and finally wormlike micelles. Increasing the local surfactant/counterion loading further promoted one-dimensional micellar growth and network-like association. When Ca²⁺ was introduced, the assembly process became slower and the final aggregate morphology shifted from elongated wormlike micelles to smaller spherical aggregates. Radial distribution functions and coordination-number analysis show that Ca²⁺ redistributes charged-group correlations within the mixed surfactant/counterion assemblies. Hydration analysis indicates enlarged polar hydration shells, whereas hydrophobic-tail hydration and gauche-defect probabilities reveal enhanced tail exposure and looser chain packing. These results demonstrate that Ca²⁺ suppresses wormlike micelle growth through coupled electrostatic redistribution, interfacial hydration, and hydrophobic-chain disorder, thereby favoring high-curvature spherical aggregates over extended wormlike networks.

NaPts-mediated headgroup organization links CO ₂ -induced protonation to multiscale self-assembly and enhanced viscoelasticity in mixed amine/zwitterionic surfactants.