Study On The Effect Of CO₂ On Emulsion Stability And Demulsification

With the popularity of CO₂ flooding technology in the oilfield,the problem of how to treat the produced fluid is followed.In this dissertation study,a self-developed high-pressure CO₂-crude mixing container was used to simulate the Changqing crude oil under simulated formation conditions.After treated by CO₂,the property of crude oil,rheology and stability of emulsion are studied by gas chromatograph,DSC,rheometer,microscope,conductivity meter and other instruments.The effect of CO₂ treatment on demulsification has been investigated and demulsifier has been screened by bottle test method.Analysis of influencing factors of demulsification has also been studied.Study on the physical properties of crude oil before and after treated by CO₂shows that the content of light components decrease,while the content of heavy components and density of crude oil increase due to extraction of CO_2.The changes of chemical composition can reduce the dissolution of wax crystal,which lead to the increase of wax appearance temperature and wax precipitation.The size of wax crystals becomes smaller and the number of them increases significantly.With the enhancement of intergranular interaction,the pour point,yield value and viscosity increases significantly,which deteriorate the low temperature rheological properties of crude oil.A brief summery about the rheology and stability of emulsion was given.The rotational speed,water content and emulsification temperature have significant effects on rheology and stability of emulsions.After CO₂ treatment,the viscosity,apparent viscosity and abnormal point increase,and the heological property deteriorate.What's more,CO₂ treatment casues increasement of conductivity of emulsion and decreasement of specific conductivity and initial delamination rate coefficient,which make the emulsion more stable.The dispersed droplets become more smaller,the shape of them become more regular,and the distribution is more uniform after treated by CO₂.With the enhancement of emulsion stability,separation of oil and water becomes more difficult.According to the experimental results,AP125 is screened as the demulsifier.After adding AP125demulsifier,the dehydration rate of the emulsion after CO₂ treatment is reduced and the demulsification difficulty is increased.However,the oil content of water is reduced after CO₂ treatment.After treated by CO₂,the dehydration rate gradually increased with the increase of the dehydration temperature,and the oil content of water also decrease.The higher the dosage,the more obvious the demulsification effect of the demulsifier.The time required for the complete removal of water droplets in the emulsion after CO₂ treatment increases.