Study On The Preparation,Dispersion Stability And Interfacial Characteristics Of Janus Polymer Nanosheets

As a new type of enhanced oil recovery technology,nanofluid flooding has the advantages of low usage concentration,strong displacement ability,good injection efficiency and little reservoir damage,which has attracted widespread attention from researchers in recent years.At present,most research is still focused on the preparation methods of nanomaterials.The dispersion stability and interface characteristics in aqueous solution are rarely reported.The dispersion stability of nanofluids is the prerequisite to ensure that they can be penetrated into reservoirs and exert oil displacement,while the interface characteristics determine the actual displacement ability of nanofluids.The focal point is to balance the dispersion stability and interfacial characteristics of nanomaterials by molecular design,so as to prepare nanofluids with excellent dispersion stability,salt resistance,and interfacial properties.Compared with conventional spherical nanoparticles or inorganic nanosheets,Janus polymer nanosheets are anisotropic in physical structure and chemical composition,which endow them with stronger functional modification capabilities and abundant dispersion and interfacial properties.However,the research on Janus polymer nanosheets is still in its infancy.Complex preparation methods,unclear dispersion and interface performance,and lack of effective theoretical guidance limit their large-scale promotion and application from laboratory to oilfield.In this paper,based on sucrose template method and emulsion interface method,two simple and efficient preparation strategies for Janus polymer nanosheets with controllable groups and adjustable sizes were established.The colloidal dispersion behavior and interface adsorption law of Janus polymer nanosheets in aqueous solution were clarified by combining experiment and simulation.Moreover,the microscopic seepage mechanism in porous media was revealed.This study could provide technical support and theoretical guidance for the molecular design,preparation method,property research and practical displacement application of Janus polymer nanosheets.Firstly,using sucrose particles as template,styrene as hydrophobic monomer,maleic anhydride as hydrophilic monomer,and oil soluble divinylbenzene as crosslinking agent,amphiphilic Janus polymer nanosheets DJPN were prepared through hydrogen bond adsorption and free radical polymerization mechanisms.This method had the advantages of reliable monomer adsorption,controllable surface chemical groups,and easy template removal.Besides,paraffin emulsion interfaces were selected as the confined twodimensional space for the self-assembly and self-orientation of amphiphilic prepolymers.Amphiphilic Janus polymer nanosheets NJPN were prepared by crosslinking with watersoluble tetraethylenepentamine.This method had the advantages of wide monomer selection,clear orientation of amphipathy,and regular lamellar surface.Both types of nanosheets exhibited distinct flexible sheet-like structures and nanoscale thickness.The lateral sizes of nanosheets could be adjusted by different power and duration of ultrasound.The surface chemical groups could be selectively regulated by types and contents of reactants.The dispersion stability and sedimentation kinetics of Janus polymer nanosheets were systematically studied by combining physical experiments and molecular dynamics simulations.The optical microrheology was introduced into the stability research of nanofluids for the first time.The abundant hydrophilic groups on the surface and their ionization process enhanced the solvation effect and effective contact area of Janus polymer nanosheets in aqueous solution.The interaction between nanosheets and surrounding water molecules was dominated by hydrogen bonding.Carboxylate ions could produce stronger hydrogen bonding than carboxylate groups in aqueous solution.The strength order between different types of amino groups was: primary amino group >secondary amino group > amide group.The structured water film on the surface of the nanosheets and the spatial effect of the polymer chains provided additional steric hindrance,which improved the dispersion stability of the Janus polymer nanosheets significantly.In addition,high temperature,high salinity,hypervalent cations and the introduction of hydrophobic carbon chains would adversely affect the dispersion stability of nanosheet suspension system.The interfacial characteristics and enhanced oil recovery performance of Janus polymer nanosheets were systematically studied by interfacial adsorption experiments,microscopic seepage experiments and core displacement experiments.Janus polymer nanosheets were equipped with excellent interfacial adsorption capacity.They could spontaneously migrate to the oil/water interface and reduce the interfacial tension.Furthermore,the formation of solid particle film enhanced the strength and deformation resistance of oil/water interface,which improved the stability of emulsion.The presence of electrolytes would squeeze the double electric layer on the surface of nanosheets,increasing the interfacial adsorption speed and total adsorption capacity.Based on the Janus polymer nanosheets,efficient nanofluid flooding systems suitable for low permeability reservoirs had been developed.Abundant hydrophilic groups and flexible sheet structure of nanosheets enhanced their injection performance.Nanosheets could self-assemble into molecular deposition films in porous media to generate wedge partial pressures and change the wettability of rock surfaces to improve oil recovery.Even at ultra-low concentrations of 0.005%,Janus polymer nanosheets could effectively improve the oil recovery,and the maximum enhanced recovery in ultra-low permeability cores reached 18.23%.