Preparation Of Carbon Dioxide Thickener And Evaluation Of Its Fracture Performance

Aiming at the fracturing treatment of the unconventional oil and gas reservoirs,two kinds of fluorine-contained thickening agents were designed and synthesized to increase liquid CO₂ viscosity for preparing the mixed systems of fracturing fluid,after we investigated a lot of research and application status of carbon dioxide fracturing fluid's thickeners at home and abroad.In this thesis,the double chain thickener and single chain thickener were synthesized with perfluorooctanoic acid,serinol,ethanolamine,1,6-hexamethylene diisocyanate and Di-tert-butyl dicarbonate as raw materials by amino protection,esterification,deprotection and nucleophilic addition reactions successively.First,the amino groups of serinol and ethanolamine were protected.Then,the perfluorinated-octanoyal chloride,which had been prepared from perfluoro octanoic acid,has been introduced into the N-Boc-serinol and tert-butyl hydroxyethylcarbamate by the esterification.Finally,after deamination protection,single and double chain thickening agent were obtained by the reaction of 1,6-hexamethylene diisocyanate with the above products.In this process,the ratios of materials in the synthesis of N-Boc-serinol and tert-butyl hydroxyethylcarbamate were optimized.The reaction temperature,time and the ratio of materials were studied through orthogonal experiments,and the optimum process conditions were identified.The intermediate products and the thickeners were characterized by FTIR spectrum,13C-NMR spectrum.The results indicated that the products were the desired products.The thermal properties,solubility in CO₂,condensate oil and water of the synthesized thickeners were determined.It was found that the double chain and single chain thickening agents's thermal properties were excellent,and the thermal decomposition occurred at 200?and 170?,respectively,which met the demands of existing shale gas reservoir.The solubility of the double chain and single chain thickeners in CO₂ were measured by static method.The data of solubility were correlated by Chrastil semiempirical model and their AARD were 9.52%and 11.14%.It can be concluded that linear fitting degree was higher,the correlation was better and the experimental measurement value was more accurate.In addition,the thickener's solubility in condensate oil and water were explored by the visual observation,in the different temperature of 40?,60? and 80?,two kinds thickening agents in condensate oil and water were not dissolved,which was easy to flow back and subsequently ground process.The thickening effect as well as the damage rates for the core of desired products in CO₂ was studied.The amount of thickening agent was obtained using single-factor method in the research.The results showed that the optimal addition of thickening agents was 2%in mass fraction.Meanwhile,the viscosity of CO₂ increased from 0.04 mPa·s to 1.54 mPa·s and 1.46 mPa·s,respectively,and the magnitudes of the increase were about a factor of 39 and 36,respectively.As the temperature increased,the viscosity of the mixed system decreased.However,the viscosity increased when the temperature increased from 30 to 40? and then decreased.Its viscosity increased as the pressure increased.With the increase of shear rate,the viscosity of the system also decreased,which belonged to a typical pseudoplastic fluid with shear thinning.The damage rates to the core permeability of the double and single chain thickening were 1.43%and 1.62%,respectively,which were far less than water-based fracturing fluid.It could meet the requirement of "Oil and gas industry standard SY/T 6367-2008 fracturing fluid general technical conditions".