Application status and research progress of CO2 fracturing fluid in petroleum engineering and its enlightenment to China: A mini-review

This paper presents a comprehensive overview of 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. However, the mining applications in China reveal that several problem areas remain unresolved: (1) The application scope of CO2 fracturing fluids is limited to the reconstruction of medium-deep wells, depleted reservoirs, and old wells with low formation pressure coefficients. (2) Different systems require different processes and ground supporting equipment due to the various types of CO2 fracturing fluids. (3) Further optimization of CO2 compatibility, functionality, temperature and salt tolerance, as well as the cost of treatment agents is needed. (4) The CO2 fracturing fluid system has low control over friction, filtration, and sand-carrying capacity. (5) There is currently no targeted industry standard evaluation system or performance evaluation method for treatment agents. In future field applications, researchers need to consider the adaptability and compatibility of existing equipment for different systems and processes while studying the mechanism of CO2 fracturing fluids. It is also essential to develop recyclable industrial-grade treatment agents, as well as low-density proppants and high-performance systems. To meet the goals of CCUS-EOR, CCUS-EGR, or fracturing displacement burial integration, optimization of the CO2 fracturing fluid fracturing design depth is necessary. This process should take into account the overall reservoir geological conditions, physical parameters, CO2 transport conditions, well site layout, and other related factors.