Preparation Of Modified Nano-polysilicon Coatings And Its Drag-reduction Performance

During the process of crude oil exploitation,the low permeability reservoir is characterized by low permeability,small pore channels and high capillary pressure,which facilitates crude oil adhering and depositing on rock pore wall when crude oil flows,increasing the resistance of oil and water flow and significantly reducing the the efficiency of oil recovery(EOR),thus becoming the bottleneck faced by petroleum engineering.The current methods of drag reduction,such as fracturing and surfactant flooding,can only improve the efficiency of water injection,but have poor effect on crude oil with high viscosity and exibit no significant increase in oil production.The modified nanopolysilicon coating owns the characteristics of good dispersion and high stability.When the painting is injected into the core,the wettability of the hole wall is improved and the flow resistance is reduced.Therefore,the preparation of modified nano-polysiloxane coating is studied in this paper,and the influence of wettability,scour resistance and drag reduction performance of core coating on stimulation oil well is analyzed,which is of great significance to the improvement of energy utilization efficiency in low permeability reservoir.A superhydrophilic/underwater superoleophobic nano-polysiloxane painting was prepared by blending method.The painting was composed of water as solvent,anionic surfactant as modifier and silica sol particles as basic structural unit.The surfactant molecules were connected to nanoparticles by simple surface grafting.It demonstrates that the best dispersion and stability are obtained by selecting spherical silica sol,sodium alysate(AOS)and alkaline conditions with the average particle size of the optimized formulation 17.18 nm,attributed to complete modification and high migration repulsive force of the nanoparticles.Dopamine was tried to be added as the cross-linking agent of the coating.Due to the self-polymerization of dopamine,a large number of hydroxyl groups were exposed on the coating surface,and the Water Contact Angle(WCA)and underwater Oil Contact Angle(OCA)of the coating surface was 0° and 157.9±1.5°,respectively,and the WCA of the coating was less than 5° after the continuous scouring of water at 100 PV(pore volume).When the painting was applied on the core,a large number of nanoparticles were attached to the core wall by the strong adsorption force of polydopamine,and the micro/nano composite structure is formed,which enhances the underwater oleophobic performance of the coating.The displacement test results show that the average drag reduction rate of the core is 11% due to the continuous formation of water film,preventing oil droplets from infiltrating into the surface.The coating exhibits the excellent efficiency of drag reduction,however,the density of the active group decreases and the surface loses hydrophilicity,due to the bonding of water and hydroxyl group during scouring.After 60 PV scouring,the pressure increases significantly,which is not conducive to the actual production process.In order to obtain the core with a better performance of drag reduction,a hydrophobic and oleophobic polysiloxane painting,containing low surface energy substances,nanoparticles,surfactants and catalysts,was prepared by sol-gel method.It demonstrates that the basic coating prepared by spherical silica sol and effective substance ratio of 6:1 without crosslinking agent increases the repulsion force and disperses evenly among nanoparticles due to sufficient hydrolysis and grafting of fluorosilane,and the average particle size is only 25.72 nm.The WCA of the coating is 154.5±1.5° and the OCA is 122.2±1.3°,and it can still keep hydrophobic and oleophobic after 100 PV scouring,performing the anti-scouring ability.After the core was modified at 60℃,the core with micro/nano composite structure was obtained by grafting with the substrate after hydrolyzing with the active group of fluorosilane.The displacement experiment shows that a lot of air cushions are in the core structure after modification,and the average rate of drag reduction is 18.7% due to the microslippage effect,and the drag reduction rate remains stable in the water flooding due to covalent bonding between the coating and the substrate.The coating has better drag reduction characteristics,but because of rough formation of the surface structure,the crude oil adheres to the surface of the coating in Wenzel state,and the pressure value will suddenly increase when it enters the displacement water,leading to serious problems such as equipment failure.In order to lessen the adhesion of oil droplets on the surface,super-slippery paintings were prepared by sol-gel method,utilizing the lubrication property of perfluorinated material to construct super-slippery coating.It demonstrates that the super-slippery painting prepared with 20 wt% alkaline catalyst,3 wt% perfluorosiloxane and 0.005 wt% fumed silica owns great dispersion and stability due to the full hydrolysis of fluorosilane,and the average particle size is only 28.8 nm.The surface structure of the coating become smooth after dip-coating,and the Oil Sliding Angle(OSA)on the coating is only 12.6±1.5°,maintaining lubrication effect after continuous scouring at 100 PV.After the coating was modified at 85℃,the surface structure of the hole wall was relatively smooth attributed to the higher content of fluorosilane,which reduced the spiking effect and enhanced the sliding property of oil droplets on the surface,with the OSA reduced to 14.6±1.3°.Covalent grafting between the coating and the core makes the OSA on the core coating change less than 5° after 10 k Pa water scouring.The displacement experiment results show that the average rate of drag reduction is increased to 36.2%,and the pressure value rises slowly and remains stable after 20 PV,due to the lubrication effect of the smooth structure on modified core.After the concentration of effective substance is reduced by 100 times,the drag reduction rate is reduced to some extent,however,because of the presence of perfluorinated substances on the surface of core,the average rate of drag reduction is still maintained at 20%,displaying the excellent drag reduction performance of this coating.