The Modification Of Silica Nanoparticles And Their Pressure-decreasing Ability Evaluation

Low abundance,low reservoir pressure,and low production are three problems that face the low permeability oil fields development.However,the harsh reservoir conditions make the injecting pressure increases quickly when water injecting is operated.How to solve this problem is the key of low permeability oil fields development.In this paper,wet modification method was employed to modify the hydrophilic silica nanoparticles from hydrophilic to hydrophobic with 3-aminopropyl-triethoxysilane（KH 550）,γ-glycidoxypropyltrimethoxysilan（KH 560）,γ-mercaptopropyltrimethoxysilane（KH 590）,N-（2-aminoethyl）-3-aminopropyltrimethoxysilane（KH 792）,vinyl triethoxysilane（A 151）,dimethyldichlorosilane（DMCS）,triethylchloro-silicane,n-propyltrichlorosilane.Titration method was employed to determine the surface hydroxyl number of silica nanoparticles.The results showed that the surface hydroxyl number decreased dramatically after modification,among them,the hydroxyl number of sample modified by DMCS decreased 81.33%after modification.Fourier infrared spectrum（FTIR）was employed to characterize the modified silica nanoparticles.The results of FTIR showed that no signal was found in the samples modified by KH 550,KH 792,A 151.Samples modified by KH 560,KH 590 had small signal,the sample modified by alkyl halosilane had strong signal.Besides,thermogravimetric analysis（TGA）,X-ray photoelectron spectroscopy（XPS）were also employed to characterize the silica nanoparticles modified by DMCS.The results confirmed that about 3%of–CH₃ had been grafted on the silica nanoparticles surface.The modified silica nanoparticles were dispersed in water with TX-100 as dispersant and NaOH to adjust the pH of the dispersion.Core flowing experiment was done to evaluate the pressure-decreasing ability of modified silica nanoparticles.Core flowing experiment results showed that silica nanoparticles modified by KH 560 and alkyl halosilane had good pressure-decreasing ability.Besides,the optimum injection amount was 1 pore volume（PV）when the concentration was 0.2%.The pressure-decreasing ability was also associated with the permeability of the cores,the pressure-decreasing percent was around 40%when the permeability of the cores was between 1×10^-3μm² and 50×10^-3μm²,it decreased to 25%when the permeability was below 1×10^-3μm².The pressure-decreasing mechanism of the modified silica nanoparticles were researched through wetting angle measurement,surface tension measurement,interface tension measurement,as well as SEM method.The surface tension of the modified silica nanoparticles was between 35 mN/m and 39 mN/m,while the interface tension between the modified silica nanoparticles dispersion and oil ranged from 2 m N/m to 6 mN/m.The soil swelling test showed that the modified silica nanoparticles can adsorb on the clay mineral surface,and went into the interlayer of clay mineral,the clay swell inhibiting percent could reach 40%.The contact angle of water to the chip treated by the modified silica nanoparticles was measured.The contact angle measurement showed that the contact angle of water to the core chip increased from 37°to more than 80°,which means that the core had changed from water wet to oil wet after treated by modified silica nanoparticles dispersion.The SEM images of core flowing channel and flowing channel surface adsorbed by modified silica nanoparticles showed that the flowing channel surface was rough original.After modification,the modified silica nanoparticles adsorbed on the core flowing channel surface,decreasing the roughness accordingly.Roughness decreasing mechanism was proposed to explain the pressure-decreasing mechanism of modified silica nanoparticles.Both hydrophilic silica nanoparticles and hydrophobic silica nanoparticles could adsorb on the core flowing channel,decreasing the roughness of the channel surface,so both of them could decrease the injecting pressure.Apart from this,the modified hydrophobic silica nanoparticles can also change the local wettability of the channel surface,make it less water wet.The critical layer thickness was decreased,and the water injecting pressure was decreased accordingly.