Nanofluid Wettability Alteration And Its Imbibition And Flow Characteristics

As a new type of medium,nanofluids are irreplaceable in terms of their properties.This study aims to study the key characteristics of sandstone reservoirs,study the nanofluid wetting reversal characteristics,nanofluid imbibition and enhanced recovery mechanism,and so on.The reservoir lays the theoretical foundation.In this paper,by means of contact angle measurement,capillary imbibition physical model,nanoparticle and oil phase microscopic interaction force,the appropriate nanofluid system is determined firstly,and the nanofluid wetting reversal characteristics and interaction force microscopic research based on atomic force microscopy(AFM)are studied.Then through nuclear magnetic resonance(NMR)experimental methods and analytical methods,based on T₂ spectrum and internal nuclear magnetic imaging of reservoir sandstone,nanofluid oil recovery degree and imbibition characteristics are studied to determine the effect of different concentrations of nanofluids,the oil recovery rate at different times of imbibition,the total degree of imbibition of different pore sizes and the change of core wettability after imbibition.Finally,by UV-visible spectrophotometer(UVS)analysis method and scanning electron microscope(SEM),quantitative,qualitative and intuitive study of nanofluid adsorption characteristics and laws in reservoirs sandstone is carried out,and the core permeability loss and adsorption retention are discussed.The results show that:(1)Si O₂ nanofluid has a significant change in wettability and even wet reversal.As the concentration of nanofluid increases,the surface hydrophilicity increases,but after the concentration reached 0.10%,the wettability doesn't have obvious change as the concentration continued to increase.The nanoparticles influence the wettability of the solid surface by the wedge structure and the structural separation pressure,which form a wedge structure at the three-phase junction,and then gradually spread and reduce the adsorption area of the oil droplet on the surface to occupy its position.From the observation of microscopic interaction force,it was further found that the nanofluid significantly reduced the adsorption force of oil on the solid surface,and the adsorption force decreased by 89.39%.(2)Nanofluids play an important role in the rapid reduction of oil saturation in reservoir cores.The higher the nanofluid concentration is,the greater the rate of decline in oil saturation is.Due to the capillary force,the nanofluid spontaneously imbibes into the small pores,and most of the discharged oil flows out through the large pores.Some oil migrates and redistributes.According to the imbibition effect,the nanofluid whose nanoparticle size is 20 nm is better than the nanofluid whose nanoparticle size is 10 nm.Within a certain range,the higher the nanofluid concentration is,the better the oil removal effect is,and the stronger the hydrophilicity of the rock after imbibition is.The droplets are not easily retained in the sandstone pores,thereby the oil recovery after the nanofluid imbibition is enhanced.(3)Adsorption experiments of nanoparticles in sandstone show that the higher the nanofluid concentration is,the greater the injection pressure and the relative permeability loss of the sandstone core are and the greater the nanoparticles adsorption and retention are.When the concentration reached 0.10%,nearly half of the nanoparticles were retained in the core;when the concentration reached 0.50%,most of the nanoparticles had irreversible adsorption.The adsorption retention position is mainly concentrated near the inlet end;the adsorption distribution of nanoparticles from the inlet end to the outlet end shows a tendency to decrease,and in one core,the closer to the exit end of the core,the greater the reduction of nanoparticle adsorption.