CO₂-soluble surfactant foam systems have gained significant attention for their potential to enhance oil recovery, particularly in tight oil reservoirs where conventional water-soluble surfactants face challenges such as poor injectability and high reservoir sensitivity. This review provides a comprehensive explanation of the basic theory of CO₂-soluble surfactant foam, its mechanism in enhanced oil recovery (EOR), and the classification and application of various CO₂-soluble surfactants. The application of these surfactants in tight oil reservoirs, where low permeability and high water sensitivity limit traditional methods, is highlighted as a promising solution to improve CO₂ mobility control and increase oil recovery. The mechanism of enhanced oil recovery by CO₂-soluble surfactant foam involves the effective reduction of CO₂ fluidity, the decrease in oil–gas flow ratio, and the stabilization of the displacement front. Foam plays a vital role in mitigating the issues of channeling and gravity separation often caused by simple CO₂ injection. The reduction in gas fluidity can be attributed to the increase in apparent viscosity and trapped gas fraction. Future research should prioritize the development of more efficient and environmentally friendly CO₂-soluble surfactants. It is essential to further explore the advantages and challenges associated with their practical applications in order to maximize their potential impact.

This study systematically analyzes the influencing factors and optimization strategies of foam stability and performance for CO₂-soluble foaming agents in high-temperature and high-pressure (HTHP) complex reservoir environments. By constructing a HTHP experimental system and utilizing dynamic foam testing, interfacial tension analysis, and microscopic observation of liquid films, the effects of chemical factors (e.g., pH, foaming agent concentration, stabilizer synergy) and physical factors (e.g., temperature, pressure) on foam behavior are investigated. The results show that the nonionic surfactant E-1312 exhibits optimal foam performance in neutral to mildly alkaline environments. The foam performance tends to saturate at around 0.5% concentration. High pressure enhances the foam stability, whereas elevated temperature significantly reduces the foam lifetime. Moreover, the addition of nano-sized foam stabilizers such as silica (SiO₂) can significantly delay liquid film drainage and strengthen interfacial mechanical properties, thereby improving foam durability. This study further reveals the key mechanisms of CO₂-soluble foaming agents in terms of interfacial behavior, liquid film evolution, and foam formation in porous media, providing theoretical guidance and optimization pathways for the molecular design and field application of CO₂ foam flooding technology.

This study investigates the behavior of heavy oil reservoirs under varying oil saturation conditions through laboratory-scale in situ combustion (ISC) physical simulation experiments. The research focuses on the propagation stability of the combustion front and key parameters influencing the in situ combustion process, with a systematic examination of crude oil composition changes and upgrading mechanisms during ISC. By employing gas chromatography (GC) and infrared spectroscopy (IR) analyses, this study evaluates the transformation of saturated hydrocarbons, aromatic hydrocarbons, resins, and asphaltenes in the produced oil before and after ISC. The results demonstrate that oil saturation plays a critical role in determining combustion efficiency, cracking dynamics, and upgrading performance. At high oil saturation (65%), combustion reactions are vigorous, yielding enhanced cracking efficiency, a significant increase in light hydrocarbon content, and effective conversion of heavy components, achieving optimal upgrading outcomes. Conversely, at low oil saturation (30%), cracking efficiency is reduced, light hydrocarbons are lost, and heavy components, including asphaltenes and polycyclic aromatic hydrocarbons, accumulate, resulting in less effective upgrading. Nonetheless, ignition and stable combustion are achievable even at low oil saturation levels. This study offers strategies to optimize ISC operations tailored to different oil saturation conditions, providing valuable insights for improving combustion efficiency and enhancing the quality of produced oil in heavy oil reservoirs.

CO₂-soluble surfactant foam systems have garnered significant attention in the fields of enhanced oil and gas recovery, environmental protection, and greenhouse gas emission reduction. This review provides a comprehensive explanation of the basic theory of CO₂-soluble surfactant foam, the mechanism of enhanced oil recovery, and the classification and application of various CO₂-soluble surfactants.The mechanism of enhanced oil recovery by CO₂-soluble surfactant foam involves the effective reduction of CO₂ fluidity, the decrease in oil-air flow ratio, and the stabilization of the displacement front. Foam plays a vital role in mitigating the issues of channeling and gravity separation often caused by simple CO₂ injection. The reduction in gas fluidity can be attributed to the increase in apparent viscosity and trapped gas fraction.Future research should prioritize the development of more efficient and environmentally-friendly CO₂-soluble surfactants. It is essential to further explore the advantages and challenges associated with their practical applications in order to maximize their potential impact.

This study investigates the behavior of heavy oil reservoirs under varying oil saturation conditions through laboratory-scale in-situ combustion (ISC) physical simulation experiments. The research focuses on the propagation stability of the combustion front and key parameters influencing the fire flooding process, with a systematic examination of crude oil composition changes and upgrading mechanisms during ISC. By employing gas chromatography (GC) and infrared spectroscopy (IR) analyses, the study evaluates the transformation of saturated hydrocarbons, aromatic hydrocarbons, resins, and asphaltenes in the produced oil before and after ISC.The results demonstrate that oil saturation plays a critical role in determining combustion efficiency, cracking dynamics, and upgrading performance. At high oil saturation (65%), combustion reactions are vigorous, yielding enhanced cracking efficiency, a significant increase in light hydrocarbon content, and effective conversion of heavy components, achieving optimal upgrading outcomes. Conversely, at low oil saturation (30%), cracking efficiency is reduced, light hydrocarbons are lost, and heavy components, including asphaltenes and polycyclic aromatic hydrocarbons, accumulate, resulting in less effective upgrading. Nonetheless, ignition and stable combustion are achievable even at low oil saturation levels.This study offers strategies to optimize ISC operations tailored to different oil saturation conditions, providing valuable insights for improving combustion efficiency and enhancing the quality of produced oil in heavy oil reservoirs.