Study On Regulation Of Silica Nanoparticles Surface Chemical Property By Using Surfactant And Imbibition Mechanism

As an important unconventional energy source,tight reservoirs have become the main battlefield in the field of petroleum exploration and development in China.In tight reservoirs,the pore properties and structures are usually complex and the connectivity is poor,resulting in low development efficiency,and imbibition method has become an important development mechanism of tight reservoirs.The surfactant has a good function of changing the interface properties and is usually used as chemical agent in imbibition experiments,but the usage and waste amount is large.Nanomaterials have special nano-effects and can improve wettability and oil recovery,but they are unstable.Therefore,using surfactants to modulate nanoparticles can obtain stable nanofluids,which is of great significance for improving oil recovery in tight reservoirs.Different types of surfactants were selected to modulate hydrophobic silica nanoparticles.Through dispersibility,temperature resistance,salt tolerance and particle size distribution experiments,surfactants were selected for the preparation of silica nanofluids.The p H value,component ratio and system concentration of the system were changed to study the regulation of surfactant surface chemistry on the surface of nanoparticles.Through imbibition experiments,the imbibition regulation of nanofluid under different permeabilities,different concentrations,different temperatures and different salinities were studied.Finally,combined with nuclear magnetic resonance imaging experiments,the functional mechanism of tight cores during imbibition process was studied.Comparing nanofluids with pure surfactant systems,the synergistic effect of nanofluids can be summed up through wetting reversal,low interfacial tension and structural separation pressure mechanism.Therefore,the imbibition mechanism of nanofluid can be studied.Considering the experimental results of dispersibility,temperature resistance,salt tolerance and particle size distribution,the non-ionic surfactant LZ1894 and nano-silica compound system are selected as experimental nano-fluids.According to the surface regulation law,the nanofluid formulation is: the p H of the system is 10,the optimum ratio of components is 1:1,and the optimal concentration of the system is 0.1 wt%.According to imbibition regulation,in the early stage of the imbibition process,the degree of recovery increases with the increase of core permeability;and when it enters the middle and late stages of imbibition,the oil recovery of core with 0.13 m D is higher than that of core with 2.23 m D.When the concentration of nanofluids increases,the ultimate recovery increases gradually,and the 0.1 wt% nanofluid has the highest recovery rate of 25.45%.Besides,the higher the temperature,the faster the imbibition oil recovery rate,and the higher the ultimate recovery rate.The cores that no longer produce oil at 25°C and 50°C were simultaneously heat up to75°C.The ultimate recovery was increased by 2.57% and 4.1%,respectively.The mineralization degree of the local layer water increases,the average particle size of the nanofluid becomes larger,and the nanoparticles are more likely to coalesce,which is not conducive to the process of seepage and drainage.Due to the synergistic effect of nanoparticles and surfactants,the wettability of rock surface can be gradually changed from oil wet to strong water wet,the equilibrium contact angle can reach 142°;the oil-water interfacial tension is reduced,and the adhesion work between crude oil and rock surface is reduced.Compared with ordinary inhalants,nanofluids also have a unique "structure separation pressure" characteristic,which makes it easier to displace oil droplets from the rock surface,and has better performance on enhanced oil recovery.