| In the process of deep formation drilling,under the action of continuous high temperature,the organic salt drilling fluid is prone to the problems of poor rheology and increased fluid loss.The addition of hydrophobic modified nano silica can effectively reduce the fluid loss of organic salt drilling fluid and improve the rheological properties to a certain extent.Therefore,the modified nano silica has a good application prospect.However,in some high-temperature,leak-prone formations,the existing nano silica treatment agent is still unable to meet the needs of drilling fluids,so the nano silica product needs to be optimized.Molecular simulation is a method to evaluate molecular action at atomic scale and then simulate various physical and chemical properties of molecular systems.Through molecular simulation,the mechanism of action of new nano silica primer can be explored.This technology can study the interaction between molecules from the micro scale,so as to reveal the law of interaction between molecules,which has a high guiding significance for the synthesis of new nano silica products.This paper forms a molecular dynamics simulation method based on Materials Studio.The solution model of(modified)nano silica and water,adsorption model of(modified)nano silica and montmorillonite,adsorption model of(modified)nano silica(Span80)and iron,friction model of(modified)nano silica and iron(montmorillonite),The mechanism of dispersion,filtration loss,inhibition and lubrication of(modified)nano silica was studied.Subsequently,the performance evaluation experiment of nano silica was carried out in this paper,and the performance test of organic salt drilling fluid after adding nano silica was carried out.The results show that the simulation method has high accuracy.Through the molecular simulation of nano silica and its performance evaluation experiment,the following conclusions are drawn:1.The main source of cohesive force of nano-silica is electrostatic force,and silane modification of nano-silica can greatly reduce its internal electrostatic effect.2.The silica hydroxyl group of nano silica is more easily adsorbated in the pores of montmorillonite,and the modified nano silica has higher adsorption energy for montmorillonite,which is more conducive to the formation of dense filter cake in the filtration process.The silane modification of nano silica will reduce the electrostatic interaction with montmorillonite,but will significantly improve the effect of van der forces.3.Nano-silica has certain inhibition,and the diffusion rate of water molecules is reduced by 12% after the addition of unmodified nano-silica.Modified nano silica has better inhibition performance because of the introduction of amino groups,which have stronger interaction with water.After the addition of modified nano silica,the diffusion rate of water molecules is reduced by 32%.4.The modified nano silica has better friction and friction compensation characteristics on the surface of iron than the unmodified nano silica.The adsorption effect on the surface of iron is stronger,and the adsorption film formed is more uniform.In addition,in the process of shear friction,compared with montmorillonite,it is more easily adsorbed on the iron surface,which is conducive to the protection of metal drilling tools.5.Nano-silica has filtration loss reduction,lubrication and inhibition properties to a certain extent in organic salt drilling fluid,and modified nano-silica has better filtration loss reduction,lubrication and inhibition properties after adding into drilling fluid,which is consistent with the simulation results.The composite modified nano silica has better dispersion properties.When the additive amount is 6%,the apparent viscosity of drilling fluid is reduced by 30%,API filtration is reduced by 48%,HTHP filtration is reduced by 29%,and lubrication coefficient is reduced by 50%.It can be used as an auxiliary fluid loss reducer,lubricant and viscosity reducer for organic salt drilling fluid. |
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