Analyzing the Mechanisms of the “Recovery” of Association Fracturing Fluids Viscosity by Molecules Self-assembly

In recent years, reports have been found of new clear fracturing fluids, a liquid system with "supramolecular structure" formulated with hydrophobically associating polymers and surfactants. Most of the reports have focused on the development and performance evaluation of the polymeric thickeners, while the mechanisms of forming molecular network and regaining viscosity through shearing of the fracturing fluids have rarely been studied. To study the mechanisms mentioned above, varied shearing rheology experiment, environmental scanning electron microscope (ESEM) experiment and proppant suspending experiment have been conducted, and the effects of molecules' self-assembly on the two mechanisms have been visually analyzed and explained. The analytical results demonstrated that the "spatial networking structure" of the association fracturing fluid is formed through the "shared" micelles between hydrophobic molecular side-chains and surfactant molecules, inter-molecular association and inter-molecular entanglement of the hydrophobically associating polymer. When shearing of the fracturing fluid is stopped, the shear-broken surfactant molecules will form new "micelles" through self-assembly, and further re-form new "networking structure" with the hydrophobic side-chains of the shear-broken hydrophobically associating polymer. "Sliding movement" between two layers of molecules causes the new "networking structure" of the "association fracturing fluid" to be in a "dynamic equilibrium" state, and to suspend proppants with much tighter "networking structure".