Experimental investigation of the entanglement network and nonlinear viscoelastic behavior of a nano-SiO2 strengthened polymer gel

Abstract

Polymer gels have been widely applied for conformance control and water shutoff in fractured and heterogeneous reservoirs. In this study, the rheological properties of a nanoparticle strengthened polymer gel were systematically studied, which was prepared by crosslinking between the hydrolyzed polyacrylamide (HPAM) and the water-soluble phenolic resin (WSPR). The primary objective of this work is to study the effects of nanoparticles on the properties of gelant and on the gelation performance. Specifically, the dispersion and degradation of polymers in the gelant were determined by dynamic light scattering (DLS) tests and rheological tests. The microstructures of gelant and polymer gel both in the presence and absence of nanoparticles were studied by Cryo scanning electron microscopy (Cryo-SEM). The results show that the nanoparticles in the gelant can effectively reduce the extent of polymer entanglement and aggregation, which would contribute to a more uniform network structure of the gel. Moreover, the nanoparticles in the gelant can increase the hydrophilicity of the polymer and inhibit the polymer degradation. The nanoparticles strengthened polymer gels also show a high strength and long-term thermal stability. The strength of gel with 0.4 wt% nanoparticles was four times higher than that of the gel without nanoparticles. The results of differential scanning calorimetry (DSC) tests also show that the addition of nanoparticles can increase the water holding capacity of the gel and efficiently restrain syneresis of the gel. Besides, the strain rate sensitivity and creep failure stress of gels were studied by large amplitude oscillatory shear tests and creep tests. The polymer gel with nanoparticles exhibits an extremely different nonlinear viscoelastic behavior, which also indicates that the structure of nanoparticle-strengthened gel has good ductility and toughness. Lastly, the nanoparticles strengthened gel has a high yield stress, which would contribute to a better blocking capacity in field applications.