Research On The Construction Of PH-responsive Oil Displacement System Based On Chitosan And The Effect Of Enhanced Oil Recovery

In order to solve the contradiction of requiring high stability of emulsion during chemical flooding and rapid demulsification in chemical flooding during oilfield development,the environmentally responsive（such as pH,temperature,CO₂/N₂,ion,light,magnetic,etc.）displacement systems consequently were introduced in recent years.The introduction of responsive system allows the stability of emulsion to be intelligently regulated by varying external environmental stimuli,enabling emulsifiers to be reuse.It is environment friendly and pollution-free.Meanwhile,the responsive system can reduce costs and increase efficiency.Particularly,the pH responsive is one of the simplest and commonly applied responsive-stimili type.In this thesis,a green and environmentally friendly polyelectrolyte chitosan is used to build pH-responsive oil displacement system.The Laser particle size analyzer,spectrophotometer,multiple light scattering,optical microscope,rheometer and other methods are used to study the properties of chitosan solutions and emulsions at different pH conditions.The results show that the emulsion exhibits the best emulsion stability at pH=6.33,whist the worst stability of emulsion appears at pH=1.51.Thus,emulsions show excellent responsiveness behavior when pH is 1.51 and 6.33,respectively.This phenomenon is correlated to the change of properties of chitosan systems at different pH conditions.Variation in pH leads to the change of degree of protonation and the charge density on the molecular chain,resulting in the association between molecules.Consequently,the emulsion type changes from normal emulsion stabilized by dissolved chitosan molecues at pH=1.51 to Pickering emulsion stabilized by chitosan particles at pH=6.33,where a higher stability displays.In addition,surfactant flooding is an important means of enhanced recovery.In order to enhance the ability of the pH-responsive emulsifier chitosan stabilized emulsion,a nonionic surfactant APG,anionic surfactant SDS,and zwitterionic surfactant BS12 were mixed with chitosan,respectively.The performance of various compounding systems and stabilized emulsions under different pH conditions were studied.The results show that a mixed adsorption layer is formed on the oil-water interface after the addition of surfactants.The viscoelasticity and stability of the emulsion stabilized by the compounding systems are enhanced compared with the emulsion stabilized by chitosan alone.The emulsion stability of the compound system also shows pH responsive behavior.Finally,the core oil displacement experiments were used to explore the oil displacement performance of chitosan and the compound systems.It shows that addition of surfactant enhances the performance of enhanced recovery of the compounding system.The chitosan/APG compounding system with pH=6.33 has the best performance of EOR,with a recovery of 19.35%.The EOR of the chitosan system alone pH=6.33 is 12.57%.These results indicate that the intelligent control of the stability of the emulsion stabilized by chitosan and its compound systems can be achieved by changing pH,which provides a new idea for the development and application of stimulus-responsive flooding systems in the oilfield development process.