Wettability Alteration And Enhanced Oil Recovery Of Surface-modification Of Si O₂ Nanoparticles

As a new kind of fluid,nanofluids are used more and more widely in the petroleum industry.Aiming at solving the problems of low permeability reservoirs,including low oil-water flow channel and large capillary pressure,the application of nano-silica?SiO₂?in enhanced oil recovery in low permeability reservoirs.Owning to the high surface energy,it is easy for SiO₂nanoparticles to aggregate.Thus,its application is limited.For further application,surface-modified is needed.Firstly,the nano-SiO₂was modified by?-mercaptopropyltrimethoxysilane?KH590?.The modified nano-silica?M-NPs?was characterized hereafter.Then,the M-NPs was studied by contact angle meter.The change of surface wettability of oil and the influence of various factors on the wettability alternation of solid surface was investigated.Furthermore,the effect of M-NPs fluid on improving the seepage recovery of low permeability reservoir as well as the influence of environmental factors were studied by core imbibition experiment.Finally,by comparing and analyzing the correlation between interfacial tension and core displacement effect,the displacing mechanism of M-NPs fluid is revealed.The results show that the optimal modification condition of nano-SiO₂is as follows.KH590 is 10%of the mass of the nanoparticles,the temperature is 70?,the time is 12 h,and the sulfhydryl group is oxidized to the sulfonic acid group by hydrogen peroxide.M-NPs display a good effect of alternating the wettability of the rock.It can change the lipophilic surface to hydrophilic one;the best effect could be achieved when the concentration of the M-NPs reaches 5000 mg/L.Moreover,its wettability changing capability is affected by environmental factors.The addition of salt reduces the ability to change wettability.In alkaline conditions,the ability to change wettability is stronger.The increase in temperature is beneficial to make the surface of the solid more hydrophilic.With the M-NPs concentration of 10000 mg/L,the seepage recovery increases as the concentration of the M-NPs increases,the ultimate recovery rate reaches more than 35%.The interfacial tension,core flooding experiments and microscopic displacement results show that M-NPs has a good ability to reduce oil-water interfacial tension and can effectively improve oil recovery on the basis of water flooding.These results indicate that the synthesized M-NPs fluid has great potential for enhanced oil recovery in low permeability reservoirs.Meanwhile,the current study provides theoretical guidance and technical support for further application of nanofluids in low permeability reservoirs.