CO₂ foam injection has been shown to be effective under reservoir conditions for enhanced oil recovery. However, its application requires a certain stability and surfactant absorbability on rock surface, and it is also associated with borehole corrosion in the presence of water. Adding surfactants to CO₂ can enhance the interaction between CO₂ and crude oil and control the CO₂ mobility, thereby improving the performance of CO₂ flooding. This paper presents a review of the research of CO₂-soluble surfactants and their applications. Molecular dynamics simulation is introduced as a tool for analyzing the behavior of the surfactants in supercritical CO₂ (scCO₂). The applications of CO₂-soluble surfactants, including CO₂ thickening, reducing miscibility pressure, and generating supercritical CO₂ foam, are discussed in detail. Moreover, some opportunities for the research and development of CO₂-soluble surfactants are proposed.

In enhanced oil recovery (EOR), various processes have specific requirements concerning surfactant surface activity. High surface activity is essential during the oil production, whereas low or even negligible surface activity is required during the oil separation process. CO₂-responsive surfactants can regulate their surface activity through the addition or removal of CO₂ in their aqueous solutions. This property makes them suitable for the formulation of CO₂-responsive displacement systems, including CO₂-responsive foam, emulsion, and hydrogel systems. These three systems hold significant application value within the realm of enhanced oil recovery. This paper reviews the structure, types, synthesis methods, applications in EOR technology, and the effects of EOR in both field and laboratory settings. This method is both environmentally friendly and efficient for enhancing oil recovery. Furthermore, the application of CO₂-responsive surfactants facilitates carbon capture, utilization, and storage, contributing to the achievement of carbon neutrality and the carbon peak.

In response to the issues of poor water flooding efficiency, low oil production rates, and low recovery rates during the high-water-cut period in the low-permeability reservoirs of the Mutou Oilfield, the non-steady-state (NSS) CO₂ huff-n-puff oil recovery technology was explored. The NSS CO₂ huff-n-puff can improve the development effect of low-permeability reservoirs by replenishing the reservoir energy and significantly increasing the crude oil mobility. Experimental investigations were carried out, including a crude oil and CO₂–crude oil swelling experiment, minimum miscibility pressure testing experiment, high-temperature and high-pressure microfluidic experiment, and NSS CO₂ huff-n-puff oil recovery on-site pilot test. The experimental results showed that the main mechanisms of NSS CO₂ huff-n-puff include dissolution, expansion, viscosity reduction, and swept volume enlargement, which can effectively mobilize the remaining oil from the various pore throats within the reservoir. The high-temperature and high-pressure microfluidic experiment achieved an ultimate recovery rate of 83.1% for NSS CO₂ huff-n-puff, which was 7.9% higher than the rate of 75.2% obtained for steady injection. This method can effectively utilize the remaining oil in the corners and edges, enlarge the swept volume, and increase the recovery rate. Field trials of NSS CO₂ huff-n-puff in a low-permeability reservoir in the Mutou Oilfield indicated that it cumulatively increased the oil production by 1134.5 tons. The achieved results and insights were systematically analyzed and could provide key technical support for the application of NSS CO₂ huff-n-puff technology in low-permeability reservoirs, promoting the innovative development of this technology.