A technical review of CO₂ flooding sweep-characteristics research advance and sweep-extend technology

The utilization and storage of CO₂ emissions from oil production and consumption in the upstream oil industry will contribute to sustainable development. CO₂ flooding is the key technology for the upstream oil industry to transition to sustainable development. However, there is a significant challenge in achieving high recovery and storage efficiency in unconventional reservoirs, particularly in underdeveloped countries. Numerous studies have indicated that the limited sweep range caused by premature gas channeling of CO₂ is a crucial bottleneck that hinders the enhancement of recovery, storage efficiency and safety. This review provides a comprehensive summary of the research and technical advancements regarding the front sweep characteristics of CO₂ during migration. It particularly focuses on the characteristics, applicable stages, and research progress of different technologies used for regulating CO₂ flooding sweep. Finally, based on the current application status and development trends, the review offers insights into the future research direction for these technologies. It is concluded that the front migration characteristics of CO₂ play a crucial role in determining the macroscopic sweep range. The focus of future research lies in achieving cross-scale correlation and information coupling of CO₂ migration processes. Currently, the influence weight of permeability, injection speed, pressure and other parameters on the characteristics of ‘fingering-gas channeling’ is still not well clear. There is an urgent need to establish prediction model and early warning mechanism that considers multi-parameters and cross-scale gas channeling degrees, in order to create effective strategies for prevention and control. There are currently three technologies available for sweep regulation: flow field intervention, mobility reduction, and gas channeling plugging. To expand the sweep effectively, it is important to systematically integrate these technologies based on their regulation characteristics and applicable stages. This can be achieved by constructing an intelligent synergistic hierarchical segmented regulation technology known as ‘flow field intervention + mobility regulation + channel plugging chemically’. This work is expected to provide valuable insights for achieving conformance control of CO₂-EOR and safe storage of CO₂.