Theoretical Study On The Properties Of Modified SiO₂ Nanoparticles For Oil Displacement

The secondary and tertiary oil recovery(EOR)of the residual oil in the pore surface and pores of oil-wet reservoirs in low-permeability reservoirs is important as an energy issue.Conventional oil displacing agents(nanoparticles and surfactants)had improved oil displacement performance and Janus granules were relatively high in preparation cost.Therefore,it is now necessary to design a new type of oil displacing agent,which is relatively simple to prepare and has excellent EOR performance.This is of great significance for the molecular design and oil displacement effect of the new oil-displacing agent,the process of reservoir exploitation and the microscopic mechanism.In this thesis,we obtained a series of modified nanoparticles by grafting a surfactant onto the surface of SiO₂ particles by molecular simulation.The performance of the modified nanoparticles(dispensability,interfacial activity and oil displacement performance)were evaluated and analyzed to reveal the effect of modified nanoparticles on EOR and the structure-activity relationship between particle structure and enhanced EOR performance.First,we investigated the dispensability of modified SiO₂ nanoparticles in aqueous solution.The results show that the modified particles by grafting the carboxylic acid surfactant had the best dispersion performance.At the same time,the disposability of the modified particles by grafting alkane surfactant,the nonionic surfactant and the zwitterion surfactant had dispersion performance partially.Then the relationship between the configuration and dispensability of different particles exhibited.The modified particles by grafting the carboxylic acid surfactant changed in the configuration of the aqueous solution,the carboxylate chain completely stretched,and the steric hindrance increased.Largely,the electrostatic repulsion between the particles enhanced greatly,and the barriers between the particles to gather were extremely high.Subsequently,the effect of modified SiO₂ nanoparticles on the oil-water interface was investigated.The effect of the modified particles was evaluated by the change in interfacial tension,and the influence of the mixed modification of the hydrophobic surfactant was further considered.Studies had shown that when the hydrophilic carboxylic acid surfactant and hydrophobic surface activity were grafted by 1:1,the particles had the strongest effect on reducing the interfacial tension between oil and water.The hydrophilic chain was folded to the water phase,and the hydrophobic chain is folded to the oil phase.The particles formed a Janus structure at the interface,the oil-water interface was thickened,and the oil-water two-phase is dissolved and enhanced.Finally,a model of residual oil droplets on the solid surface and oil molecules in the reservoir pores was constructed to evaluate the EOR performance of the mixed modified SiO₂ nanoparticles.The oil displacement performance depended on reducing the oil-water interfacial tension,weakening the cohesive energy of the oil molecules,and weakening the adsorption strength of the oil molecules on the surface of the reservoir.For Hydrophobic surface and reservoir channels,the structure-activity relationship between the particle structure and the oil displacement performance had important guiding significance for the design and preparation of the nanoparticle oil displacement agent.