CO_(2)响应型清洁压裂液性能及其转变机理分析

Performance and Transformation Mechanism of CO_(2) Responsive Clean Fracturing Fluid

为改善水力压裂返排液对储层的伤害和环境的污染,以硬脂酸与N,N-二甲氨基丙胺为原料、氟化钠为催化剂,通过双分子亲核取代反应制备了具有CO_(2)响应的表面活性剂(EA)。将其与反离子水杨酸钠复配制备具有CO_(2)响应增黏的水溶液体系,可作为清洁压裂液体系实现循环利用。利用流变仪研究了EA水溶液及其与反离子复配体系的CO_(2)响应性和循环可逆性,利用电子显微镜和分子动力学模拟从介观和微观层面揭示其响应及可逆转变机理。结果表明,EA水溶液及复配体系均具有良好的CO_(2)和pH响应增黏特性,通入N_(2)或高温可实现体系降黏。该溶液体系的CO_(2)响应增黏率高、响应速度快、黏弹性模量高,可以实现多次可逆转变。分子动力学模拟及冷冻电镜揭示了溶液体系中蠕虫状聚集体的形成及转变机理,为实现清洁压裂液循环利用提供理论基础。

In order to improve the damage of hydraulic fracturing flow-back fluid to reservoir and the pollution to environment,the surfactant EAwas synthesized by bimolecular nucleophilic substitution reaction with stearic acid and N,N-dimethylaminopropylamine as raw materials and sodium fluoride as catalyst.An CO_(2) responsive aqueous solution was constructed by mixing sodium salicylate and EA,which could be used as clean fracturing fluid and realize recycling.The reactivity and cyclic reversibility of EA aqueous solution and its compound system with counter ion were evaluated by rheometer.The responsive and reversible transformation mechanism were analyzed from mesoscopic and microscopic levels by electron microscope and molecular dynamics simulation.The results showed that EA aqueous solution and the compound system had good viscosity increasing characteristics to the response of CO_(2) and pH value,and the viscosity reduction of system could be realized by introducing N_(2) or high temperature.The solution system had high viscosity increasing rate to CO_(2) response,fast responsive speed and high viscoelastic modulus,and could realize multiple reversible transformations.Molecular dynamics simulation and freeze electron microscope revealed the formation and transformation mechanism of wormlike aggregates in solution system,which provided a theoretical basis for the recycling of clean fracturing fluid.