Application status and research progress of CO_(2) fracturing fluid in petroleum engineering:A brief review

This paper comprehensively reviews the application and research progress of CO_(2) fracturing fluids in China,highlights the existing issues and puts forward suggestions for future development.Three types of fracturing fluid systems containing CO_(2),namely,CO_(2) dry fracturing fluid,CO_(2) energized fracturing fluid,and CO_(2) foam fracturing fluid,are categorized based on the mass ratio and process difference between CO_(2),water,and treatment agents.Field applications in China reveal several problem to be resolved:(1)The application scope of CO_(2) fracturing fluids is restricted to depleted reservoirs,re-fracturing of old wells,and medium-deep reservoirs with low formation pressure coefficients;(2)different types of CO_(2) fracturing fluids require different processes and ground supporting equipment;(3)optimization of CO_(2) compatibility,functionality,temperature and salt tolerance,as well as the cost of treatment agents is necessitated;(4)existing CO_(2) fracturing fluid system fail to perform well with low friction,low filtration,and high sand-carrying capacity.(5)there lacks a targeted industry standard for evaluation of performance of CO_(2) fracturing fluid system and treatment agents.Therefore,in order to meet the goals of CCUS-EOR,CCUS-EGR,or integration of fracturing,displacement and burial by CO_(2),efforts should be made in the aspects that followed,including in-depth investigation of the mechanism of CO_(2) fracturing fluids,the adaptability and compatibility between existing equipment,different CO_(2) fracturing fluid systems and processes,and construction of treatment agents,low-density proppants and highperformance systems of recyclability and industrial-grade.In addition,optimization of CO_(2) fracturing fluid system based fracturing design is also crucial taking such related factors such as overall reservoir geological conditions,petrophysical properties,CO_(2) transportation,and well site layout into consideration.