Preparation And Pressure Reduction Mechanism Of Ultra-small Size Carbon Silicon Composite Nanoparticles

Low permeability/ultra-low permeability reservoirs have developed micro-nano pore throats,low permeability and serious heterogeneity.Natural energy production decreases rapidly and energy supplement is difficult.Water injection is the most economical and feasible way to supplement formation energy for a long time.However,due to the small matrix pore throat and the adhesion of oil film on the wall,combined with the hydration and expansion of reservoir clay caused by water injection,the throat is blocked,resulting in high water injection pressure and serious’high pressure underinjection’problem.Nanomaterial drag reduction and injection enhancement technology is the most likely solution to this problem by nanomaterial adsorption on the surface of formation rock to reduce water injection pressure.However,due to the limitation of industrial preparation process,the traditional Si O₂ nanoparticles are often of large particle size（?15 nm）,poor uniformity,poor dispersion and stability,easy to agglomerate and settle,poor matching with micro-nano pore throats in ultra-low permeability reservoirs,and complex surface modification.Therefore,it is urgent to develop a low-cost and easy-to-obtain nanomaterial with ultra-small size（?5 nm）,good uniformity and self-stable dispersion,and establish a new drag reduction method for micro-nano pore throats in ultra-low permeability reservoirs.Carbon-silicon composite nanomaterials have great application potential due to their mild reaction,controllable particle size,good dispersion and rich surface groups.In this paper,the carbon source and silicon source structures were optimized,and the reaction conditions were optimized to obtain the preparation method of ultra-small nanoparticles with controllable reaction kinetics.After the synthesis of series of nanoparticles,the influence of different factors on the dispersion of nanoparticles was studied by dynamic light scattering instrument to reveal the thermodynamic stability of nanofluids.Secondly,the adsorption behavior of nanoparticles at solid-liquid interface was studied by UV spectrophotometer and interfacial rheometer,and the distribution and rheological properties of nanoparticles at oil-water interface were explored to reveal the interfacial adsorption characteristics of nanofluids.Based on the core displacement experiment,the drag reduction effect of nanofluids under different factors was studied to clarify its drag reduction law.Finally,the effect of particles on wall morphology,roughness and micro-wettability at pore scale was quantitatively analyzed by atomic force microscopy.The effect of particles on the shear force field around the oil-water interface was studied by using the visual microscopic pore throat model and the microparticle microvelocimetry.The drag reduction mechanism of carbon-silicon composite nanofluids was revealed from the perspectives of solid-liquid and liquid-liquid interface regulation.After optimization,it was confirmed that D-GT was the carbon source and APTES was the silicon source.The reaction nucleation rate of the two was 11%-16%of that of the nano-Si O2 prepared by chemical precipitation method,which could effectively regulate the particle size of the product.Synthesizing the particle size,stability and yield of the product,the reaction conditions were selected as follows:temperature 50°C,time 6 h,speed 200 rpm.The uniform and well-dispersed nanoparticles with average particle size of 2.7 nm and size variance of 0.13were obtained.The carbon and nitrogen elements on the surface of the product accounted for about 60%,and the organic groups were mainly amino and carbonyl with many active sites.Nanoparticles can be adsorbed on the solid-liquid interface to form an adsorption layer,which reduces the roughness of the pore wall by 29.24%and increases the micro-wetting homogeneity by 2.45 times,resulting in a significant decrease in the strong wall adhesion sites and a 39%decrease in the oil phase adhesion.Nanoparticles adsorbed on the oil-water interface to form a thin film,which reduced the interfacial tension by 43%.At the same time,the interface was solidified,resulting in the shear force increased by 1.72 times when the fluid scoured the oil film.The above synergy makes the oil film easier to be peeled off,broadens the effective channel radius,and reduces the viscous force loss during fluid flow.In the saturated oil-rock core with permeability of 0.26-5.05 m D,the drag reduction rate of carbon-silicon composite nanofluid can reach 25.38%-30.45%.