| With the further development of oil exploration,more and more complex strata which are difficult to exploit before are founded.In order to ensure efficient oil exploration,higher requirements on drilling technology,especially on drilling fluid treatment agent is needed.Borehole stability is one of the most important conditions in the drilling process,and the borehole stability is closely related to shale stability.Shale has the characteristics of low permeability,micro-pores and micro-fractures,and The size of traditional drilling fluid sealing agents has poor sealing effect on shale nanoscale pores.In recent years,the combination of nanotechnology and drilling technology has accelerated the development of the oil drilling industry.Nanomaterials are easy to enter shale micro-fractures,which can form a tight plugging layer to effectively seal,prevent filtrate from entering shale,and improve formation bearing capacity and borehole stability.Nano-particles have small size,large specific surface area,quantum size effect and macroscopic quantum tunneling effect.Compared with similar materials,it shows stronger physical and chemical properties.Nano silica has been widely studied and applied in oil drilling for its advantages of environmental protection,low price,high thermal stability,easy modification and strong adaptability.Due to the high specific surface area and surface energy of nano-silica containing a large amount of silica-hydroxyl group,it is easy for the silica-hydroxyl group to condense.These particles are easy to aggregate and precipitate in the water suspension,and lose the nano-size,which affects the application in water-based drilling fluid.Therefore,the performance of nano-silica can be optimized by modification.Silane coupling agent is a commonly used and effective surface modifier for nano silica.The physical parameter information of silane coupling agent is very important for the identification and control of material properties in chemical engineering.The determination of property parameters by experiment is time-consuming and laborious,and the accuracy of data is limited by the variety of methods,the repetition and reproducibility of results,and the reliability of equipment.Quantitative structure-property/activity relationships(QSPR/QSAR)can be used to establish quantitative relationship models between compound structures and biological activities/properties.Thus,the activity/properties of the compound can be predicted.Hologram QSAR(HQSAR)is a novel and effective quantitative structure-activity relationship method with simple modeling,fast calculation and high prediction accuracy.Firstly,QSPR models of silane coupling agent and its related properties were established based on HQSAR method.These models can predict the property parameters of silane coupling agent,and can also preliminarily screen a large number of silane compounds,providing technical support for the study of modification technology of nano silica,which has a guiding effect on the future oriented design of silane coupling agent.Secondly,nano silica was modified by the common silane coupling agent KH-570 to improve the dispersion of nano silica.Finally,the rheological properties,fluid loss reduction,lubricity and inhibition of nano silica plugging agent in bentonite-based slurry and drilling fluid system before and after modification were evaluated.Specific work is as follows:The HQSAR model of silane coupling agent and refraction rate and density was established.The predictive power of the evaluation model was verified by leaving a cross-validation and an external test set.The results show that the established HQSAR models have good predictive ability.Through the molecular contribution diagram of the models,the structural groups that affect the refractive value of silane coupling agent and benzene ring substitution in the molecules are founded.The presence of long chain alkyl groups on the base and oxygen atoms will increase the refractive value.The surface performance of nano silica plugging agent was optimized by KH-570.Firstly,the dispersion stability of modified nano silica in aqueous medium was analyzed by sedimentation method.The results show that the optimized nano silica particles have higher dispersion after modification.Secondly,the influence of KH-570 dosage,reaction temperature and reaction time on the size of nano silica particles were investigated.Finally,the optimal modification conditions of nano-silica were as follows: the dosage of KH-570 was 8.0 wt.%,the modification time was 2 h,and the modification temperature was 70 ℃.Under these conditions,the optimized nano silica has the smallest particle size in the aqueous phase,with an average particle size of 152.19 nm.Rheological properties,fluid loss reduction,lubricity and inhibition of nano silica plugging agent in bentonite slurry before and after modification were evaluated.The results showed that the modified silica has better filtration loss performance in bentonite-based slurry.The mud cake formed by modified nano silica is smooth,compact and has no cracks.The lubricity of modified nano silica sealer is better than that of unmodified nano silica sealer.Compared with unmodified nano silica,the modified nano silica has better inhibition on the hydration expansion degree of clay.The rheological properties,fluid loss reduction,lubrication and inhibition of nano silica plugging agent before and after modification in drilling fluid system were evaluated.The results show that the modified nano silica can greatly improve the apparent viscosity and plastic viscosity of drilling fluid,but has little effect on the dynamic shear force.The modified nano silica still has a good effect on filtrate loss in drilling fluid system.The lubricity of modified nano silica plugging agent in drilling fluid system is poor.The modified nano silica showed good inhibitory properties in drilling fluid. |
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