Synergistic Effect Between Wormlike Micelles and Nanoparticles in Stabilizing Foams for High Temperature Stimulation

Abstract

Abstract As the resulting foam is unstable both thermodynamically and kinetically, its volume decays with time once foam generation is stopped. Lack of stability of these foams often limits their application. The current study attempts to investigate the synergistic effect of using elongated wormlike micelles and silica nanoparticles on foams stability. And foams with better performance as a fracturing fluid can be conducive to efficient stimulation under harsh formation conditions. First, the stability of static foams was studied using a blend of cationic foaming agent (CTAB) and wormlike micelles zwitterionic surfactant (EAPB) with and without silica nanoparticles. Second, in order to figure out the stability mechanism, bubble size distribution, film thickness, micro structure were conducted by optical microscope and cryo-scanning electron microscopy (cryo-SEM) while free drainage, viscoelasticity and rheology experiments were carried out for confirming the conclusion. Finally, proppant suspension experiment with silica nanoparticles over time was measured at high temperature to verify the synergistic effect between elongated wormlike micelles and silica nanoparticles. With silica nanoparticles and elongated wormlike micelles, foams exhibited a significant improvement in stability especially at high temperature. As the three main mechanisms operating during and after the production of foams are drainage, coalescence and coarsening, irreversible adsorption on gas-liquid interface of silica nanoparticles could improve the elasticity of foam films and elongated wormlike micelles could enhance the fluid viscosity at the same time. They remarkably delayed above three processes, showing synergistic effect in stabilizing foams, corresponding to uniform and small bubble size, thick foam films, dense micelle structures and slow drainage rate. Under high temperature and shearing stress, the viscosity of foam began to rise at first which may result from the network formation consisting of micelles-nanoparticles junctions. This corresponded to an increase in viscoelasticity when adding silica nanoparticles. However, once association between micelles and silica nanoparticles broke, there was a continued decrease in viscosity. The proppant suspension experiment showed that although free drainage stopped and foams became unstable, the presence of nanoparticles aggregates together inducing traffic jam in Plateau border, slowing the drainage rate which dominates the velocity of settling proppant. Therefore, the settlement of proppant could be hindered because of physical resistance of nanoparticles. With enhanced performance, foams employed as a fracturing fluid exhibit extraordinary characteristics in terms of stability, rheology and proppant suspension ability at high temperature. It is worth pointing out that nanoparticles will have a broad prospect in stimulation field.