一种新型的CO2响应性凝胶封窜体系

A new type of CO2 responsive gel based channeling blocking system

针对低渗透油藏CO2驱开发后期的气窜问题,利用小分子胺类化合物和一种改性长链烷基阴离子表面活性剂制备了新型CO2响应性凝胶封窜体系。在不同温度(25℃、70℃)、不同压力(常压、8 MPa)下对体系接触CO2前后的流变性进行了测试,利用环境扫描电镜和核磁共振表征了其微观结构,通过岩心物理模拟实验评价了体系的封窜性能。实验结果表明,体系在接触CO2前为黏度与水相近的溶液,接触CO2之后则转变为高黏凝胶状态,且表现出黏弹性;接触CO2后体系内部结构由松散分离的无序排列转变为排列有序紧密连接,形成三维网状聚集结构。核磁共振测试结果证实了体系接触CO2之后小分子胺类化合物发生质子化的现象,形成“伪双子表面活性剂”,再通过自组装聚集缠绕形成蠕虫状胶束,造成体系接触CO2后黏度急剧增大。高低渗双管并联岩心实验表明,多孔介质条件下该体系对于高渗岩心的封堵率大于90%。研究结果为低渗储层CO2驱开发后期的气窜封堵提供了技术指导。

In order to solve the gas channeling problem in the late stage of CO2 flooding in low-permeability reservoirs,a new type of CO2 responsive gel based channeling blocking system was prepared by using small-molecule amine compound and a kind of modified long-chain alkyl anionic surfactant.Then,the rheological property of this system before and after contacting CO2 was tested under different temperatures(25℃and 70℃)and different pressures(normal pressure and 8 MPa),and its microscopic structure was characterized by means of environmental scanning electron microscope(ESEM)and nuclear magnetic resonance(NMR).And in addition,its channeling blocking performance was evaluated by virtue of core physical simulation experiment.The experimental results show that before contacting CO2,this system is a kind of solution whose viscosity is close to that of water,and after contacting CO2,it transforms into high-viscosity gel with viscoelasticity.And after this system contacts CO2,its internal structure is transformed into tightly-connected ordered arrangement from loosely-separated random arrangement,and a 3D network aggregation structure is formed.NMR test results prove that after this system contacts CO2,small-molecule amine compound is protonated to form the“pseudo Gemini surfactant”and then vermicular micelle is formed through self-assembly,aggregation and winding,which leads to the sharp increase of the viscosity.High-low permeability double tubes parallel core experiment indicates that under the condition of porous medium,the blocking rate of this system to high-permeability core is higher than 90%.The research results provide technical guidance for the gas channeling blocking in the late stage of CO2 flooding in low-permeability reservoirs.