Research And Application Of Modified Nano Silica In Water-Based Drilling Fluid

One of the key links in the process of drilling is to maintain the stability of wellbore.70%of the borehole wall instability is related to the instability of the shale.Shale formation is characteristic with low permeability,micropores and microcracks,which results that plugging agent of the traditional drilling fluid can not achieve the good sealing effect on the micropores and microcracks of the shale because of the size.The wide application of nanometer material provides the possibility solving the difficult problem of micro fracture plugging technology.Nano-material is also called ultrafine particles and generally refers to the size between 1-100 nanometer particles.The unique nano-effect of nanometer material in size,surface activity and other aspects provides an advantage on applying in the drilling fluid.Numerous studies have shown that adding micro-nanomaterials to the drilling fluid maybe effectively block the microglores and cracks of shale and maintain the stability of the wellbore.But the surface hydroxyl groups on the surface of nano materials are prone to be condensed,resulting in agglomeration and losing the nanometer size,which affects its application in drilling fluid seriously.Therefore,the study of the dispersion technology of nanomaterials and the performance of effective sealing micropores and microcracks have great practical value and theoretical significance.In this paper,aimed at the plugging of shale microfracture in the process of drilling,nanometer silicon dioxide was applied to water-based drilling fluid to achieve the effective sealing of shale micro-cracks and the surface modification of nanometer silicon dioxide was used to solve dispersion problem existing in the application of nanomaterial.Nano silica was composite modified by silane coupling agent and wetting reversal agent twelve sodium sulfate?SDS?.The modified nano-silica was characterized by modern analytical methods,such as Fourier transform infrared spectroscopy?Fr-IR?,Transmission electron microscope?TEM?,and Nanometer laser particle size analyzerto analyse the effect of modification.Fourier transform infrared spectroscopy showed that the absorption peak of Si-OH on the modified nano-silica was obviously weakened and the surface hydroxy groups of SiO₂ had been partially involved in the reaction.The morphology and dispersion of modified Nano silica in aqueous solution were evaluated by Transmission electron microscopy?TEM?experimental.Experiments show that the modified nano silica in aqueous solution are spherical and has uniform size distribution and good dispersibility in water,and the particle size was less than 100 nm.In addition,the dispersion properties of modified nano-silica materials in aqueous phase and water-based bentonite slurry were evaluated by Nanometer laser particle size analyzer and sedimentation performance analysis experiment.The experimental results show that the modified nano-silica material has better dispersibility in the aqueous phase and the water-based bentonite slurry and particle size distribution in 30-120 nm and 40-120 nm.The performance of modified nano-silica in sealing,filtration loss,inhibition,lubricity and anti-high temperature were evaluated.The results show that the modified nano-silica in the water-based bentonite slurry has certain ability of lowering filtration,restraining the swelling of the clay and improving the lubricating.What more,it has good anti-high temperature performance.The high temperature and high pressure nano filtration membrane experiment and artificial mud cake experiment were carried to simulated formation micro cracks and evaluate the sealing performance of modified nano-silica.The data of high temperature and high pressure nano filtration membrane experiment show that the high temperature and high pressure nanofiltration membrane loss of filtration of drilling fluid with modified nano-silica reduce23.07 percent;The artificial mud cake experiment results show that the permeability of artificial mud cake is reduced by 85.4%.Therefore,modified nano-silica can achieve effective blocking of micro-cracks in the shale.Through optimizing the tackifier,fluid loss agent,inhibitor and other treatment agent to determine the drilling fluid formula is:4%bentonite slurry+0.4%PAM+0.3%FA367+2%WGF-1+2%SPNH+1%MCH+2%SLR-2+2%MNP.The drilling fluid system not only has the advantages of high temperature resistant,and good inhibitional property,but also can resist temperature 140? and anti-pollution up to 8%NaCl,2%CaCl₂ and 0.5%MgCl₂.