Preparation And Action Mechanism Of Nanoparticle/Amphiphilic Polymer Composite Gel

Many oilfields around the world are using enhanced oil recovery（EOR）methods to maximize oil production.Carbon dioxide flooding in low permeability reservoirs faces fractures and gas channeling.Application of polymer gels can alleviate this problem.However,an acidic environment was formed due to CO₂ flooding.Current polymer gels cannot resist acidic conditions,high salinity（Na Cl 150000 mg/L,Ca Cl₂ 8000 mg/L,Mg Cl₂ 8000 mg/L）and high temperature conditions.In this study,an amphiphilic polymer and a crosslinking agent（hexamethylenetetramine and hydroquinone）were used to propose and optimize a nanosilica amphiphilic polymer composite gel under acidic and harsh reservoir conditions.This study provide basic data,gel mechanism and theoretical guidance for practical applications.A nanosilica amphiphilic polymer composite gel was developed using amphiphilic polymers,crosslinking agents（resorcinol and hexamethylenetetramine）,silica,and anionic surfactants.The surfactant-free gel was further optimized by changing the acidic conditions of the crosslinking agent.The optimal formulation of nanosilica amphiphilic polymer composite gel was determined using amphiphilic polymers,crosslinking agents（hexamethylenetetramine,hydroquinone）,and silica under the acidic and high salinity conditions.The effects of temperature,gel time and gel strength on the gel properties were studied using the bottle test method.Based on the gelation mechanism,Si O₂ and organic gel were compounded to optimize the preparation of high-strength nanosilica amphiphilic polymer composite gel.The scanning electron microscope（SEM）was used to study its microstructure.The micro-rheometer was used to in-situ evaluate the elasticity index（EI）and mean square displacement（MSD）of the nanosilica amphiphilic polymer composite gel system.Finally,the plugging performance was evaluated to explore the feasibility of the application.The results show that nanosilica amphiphilic polymer composite gels can significantly improve gel strength compared with organic amphiphilic polymer gel.Si O₂ can effectively enhance gelation and maintain thermal stability for a long time.The elasticity of the nanosilica amphiphilic polymer composite gel is enhanced by Si O₂,and the silica is adsorbed on the hydrophobic association structure of the amphiphilic polymer through electric attraction and hydrogen bonding,which enhances the plasticity of the microstructure spatial network and makes the solution viscoelastic.The optimal concentration of the nanosilica amphiphilic polymer composite gel formulation is amphiphilic polymer 4000 mg/,Si O₂ 3000 mg/L and HQ/HMTA 4000 mg/L.This gel has a strength of 0.062 MPa at 80℃and a thermal stability of 60days（salinity 150000 mg/L of sodium chloride,8000 mg/L of magnesium chloride and 8000mg/L of calcium chloride）.The gelation time is 119 hours.From neutral to acidic conditions,gel strength and viscoelasticity increase with increasing amphiphilic polymer,crosslinker,silica,salinity,and p H.The micro-rheological measurement results show that the higher the Si O₂concentration,the shorter the plateau period,and the higher the elasticity index of 10^-3nm^-2.The nanosilica amphiphilic polymer composite gel has good spatial structure and good water retention under acidic conditions.Under high,medium and low permeability conditions,the plugging rates of the sand-packs reaching critical breakthrough pressures were 98.3%,97.1%and 86.7%,respectively.The results show that this method can successfully plug the hypertonic layer.The nanosilica amphiphilic polymer composite gel has good thermal stability,high strength,pressure resistance,and plugging effects as well as has good application potentials in acidic and high salinity reservoirs.