Synthesis,Evaluation And Application Of Modified Nano Silica Plugging Agent

With the development of oil and gas in shale formation,the wellbore wall is unstable due to its low permeability,micro-pores and micro-fractures during drilling.Well wall stability is crucial to oil and gas production.Traditional drilling fluid plugging agents are not effective in shale formations,so nanomaterials are needed to achieve better results.In recent years,nanomaterials have become the focus of oilfield developers.Nanomaterials,also known as ultrafine particle materials,typically range in size from1-100 nm.Because of its unique nano effect,it has been widely used in drilling fluid.Studies have shown that adding these micro-nanomaterials to drilling fluid can effectively seal shale micropores and fractures,thereby maintaining wellbore stability.However,agglomeration and agglutination occurred among particles due to silica-hydroxyl polymerization,which affected the plugging effect of drilling fluid.The surface of nano silicon dioxide was modified by using anhydrous ethanol as dispersing agent,nano silicon dioxide as silicon source and silane coupling agent KH-550 as surface modifier.Fourier infrared spectroscopy,particle size analyzer and transmission electron microscopy were used to characterize the molecular structure,particle size distribution and morphological characteristics of the modified nano silica.Fourier infrared spectroscopy showed that the number of hydroxyl groups on the surface of the modified nano silica decreased.The morphology and dispersion of nano silica in aqueous solution before and after modification were evaluated by transmission electron microscopy.The experimental results show that the particle size distribution of the modified nano silica is uniform in aqueous solution,and the dispersion in water is good,and the particle size is less than 100 nm.The dispersion properties of modified nano-silica materials in aqueous phase and drilling fluid bentonite slurry were evaluated by Omni multi-angle particle size and high-sensitivity Zeta potential analyzer.The experimental results showed that the particle size distributions of modified nano-silica materials in aqueous phase and drilling fluid bentonite slurry were 70-80nm and 70-120 nm,respectively.The experiment shows that the modification of silane coupling agent can effectively improve the dispersion of nano silica in aqueous phase.The performances of modified nano-silica in drilling fluid base slurry,such as plugging,filtration loss reduction,inhibition,lubricity,high temperature resistance,pollution resistance were evaluated.The experiments showed that the modified nano-silica could not only improve the inhibition and lubricity of drilling fluid base slurry,but also improve the filtration reduction performance of drilling fluid base slurry.The experiments proved that the modified nano-silica could achieve effective plugging of shale micro-fractures.Through the optimization of tackifier,filtration loss reducer,inhibitor and other treatment agents,the drilling fluid formula was determined:2%bentonite+0.3%xanthan gum+0.5%NAT-20+1.5%NAF-25+0.5%SFT-2+10%KCl.The drilling fluid system has good inhibition performance and temperature resistance.It can withstand temperature of 140°C,has a certain ability to resist inorganic salt pollution,and is resistant to 8% NaCl and 2% CaCl₂.