Research Of Modified Nanoparticle-Enhanced Clean Fracturing Fluid And Enhancement Mechanism

Due to high viscoelasticity and little residue,clean fracturing fluid system based on viscoelastic surfactant has been receiving increasing attention.However,during the application of it,problems of clean fracturing fluid are becoming obviously,such as poor temperature resistance and high filtration loss.It has been shown that the addition of nanoparticles can effectively improve rheological properties of the fracturing fluid.However,normal nanoparticles have problem of weak synergistic effect with common viscoelastic surfactants,which can lead to low enhancement efficiency.Further research shows that modified nanoparticle can have better enhancement on specific surfactant molecules than normal nanoparticles.However,the exisiting modification method of nanoparticles have complex synthesis process and demanding strict environment.Therefore,preparing a newly kind of nanoparticle-enhanced viscoelastic surfactant clean fracturing fluid system,which can simplify synthesis process of modified nanoparticles,optimize the molecular structure of surfactant and further strengthen attraction force between surfactant molecules and nanoparticles,is one of potential methods for broadening the scope of nanomateries applied in fracturing process.Here,a simple anhydride-modified nanoparticle synthesis method and route was established by chemical wet modification and esterification with anhydride and hydrophilic silica nanoparticles.In addition,according to the effect of modification,dispersity,cost and physicochemical properties of synthetic source,succinic anhydride-modified silica nanoparticle（SAM-SNP）can be selected out as the enhancer of clean fracturing fluid.Besides,polyhydroxy cationic quaternary ammonium surfactants C₁₆DHAB and C₁₈DHAB are prepared by a single step of reaction,with better water solubility and rheological properties than conventional surfactants.After that,based on composition and optimiazation of concentration,the best rheological wormlike micellar system 4 wt%C₁₈DHAB+0.9 wt%NaSal was constructed.Finally,the wormlike micellar system and SAM-SNP were mixed and the best enhancing of viscosity system 0.1 wt%SAM-SNP+4 wt%C₁₈DHAB+0.9 wt%NaSal was determined as the formula of modified nanoparticle-enhanced clean fracturing fluid system.The results of fracturing fluid performance evaluation show that modified nanoparticle-enhanced clean fracturing fluid system has larger consistency coefficient than that of normal clean fracturing fluid.In addition,modified nanoparticle-enhanced clean fracturing fluid system has excellent viscoelasticity,temperature-shearing resistance（up to 92℃）,good shearing restoration,strong prop-carrying capacity and easy breaking property.In addition,the result of physical simulation experiment demonstrates that though the system has low damage to permeability of core,it can leave the adsorption of nanoparticles on the surface of core and reduce filtration of fracturing fluid.The research of enhancement mechanism shows that the growth of wormlike micelles induced by nanoparticles is the essence of enhancement.The enhancement of SAM-SNP is greatly better than that of normal silica nanoparticle.This is because that SAM-SNP has better dispersity in water,larger ionization degree and stronger attraction force with surfactant molecules caused by electrostatic attraction and hydrogen bonding.Above all,it can benefit form more stable and strong nanoparticle-micelle junctions and double network structure.