Application status and research progress of CO2 fracturing fluid in petroleum engineering: A brief review

This paper comprehensively reviews the application and research progress of CO₂ fracturing fluids in China, highlights the existing issues and puts forward suggestions for future development. Three types of fracturing fluid systems containing CO₂, namely, CO₂ dry fracturing fluid, CO₂ energized fracturing fluid, and CO₂ foam fracturing fluid, are categorized based on the mass ratio and process difference between CO₂, water, and treatment agents. Field applications in China reveal several problem to be resolved: (1) The application scope of CO₂ 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 CO₂ fracturing fluids require different processes and ground supporting equipment; (3) optimization of CO₂ compatibility, functionality, temperature and salt tolerance, as well as the cost of treatment agents is necessitated; (4) existing CO₂ 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 CO₂ 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 CO₂, efforts should be made in the aspects that followed, including in-depth investigation of the mechanism of CO₂ fracturing fluids, the adaptability and compatibility between existing equipment, different CO₂ fracturing fluid systems and processes, and construction of treatment agents, low-density proppants and high-performance systems of recyclability and industrial-grade. In addition, optimization of CO₂ fracturing fluid system based fracturing design is also crucial taking such related factors such as overall reservoir geological conditions, petrophysical properties, CO₂ transportation, and well site layout into consideration.