Advances in CO2 Foam for Profile Control, Enhanced Oil Recovery, and Carbon Storage in Low-Permeability and Tight Oil Reservoirs

Abstract

: Low-permeability and tight oil reservoirs are characterized by small pore-throat sizes and strong heterogeneity. During the process of conventional CO 2 flooding, viscous fingering, gravity override, and gas channeling through preferential flow paths are prone to occur, resulting in insufficient sweep efficiency, low CO 2 utilization, and reduced storage efficiency. CO 2 foam can divide the continuous CO 2 gas phase into numerous discrete bubbles, thereby increasing the apparent gas viscosity and reducing the effective gas mobility. Therefore, it has great application potential in profile control, gas-channeling mitigation, enhanced oil recovery (EOR), and geological CO 2 storage. Focusing on the requirements of CO 2 foam flooding and the synergistic development of carbon capture, utilization, and storage-enhanced oil recovery (CCUS-EOR) in low-permeability and tight oil reservoirs, this paper systematically reviews the physicochemical fundamentals, static and dynamic performance evaluation methods, and commonly used foaming systems of CO 2 foam. Particular attention is paid to the foam-stabilizing characteristics and reservoir applicability of surfactant foams, nanoparticle-surfactant composite foams, and related systems. On this basis, the mechanisms of CO 2 foam mobility control and gas-channeling mitigation in porous media are analyzed, and the processes by which foam expands sweep volume through gas-phase division, pore-throat blockage, and selective plugging are clarified. Meanwhile, the main mechanisms by which CO 2 foam improves microscopic displacement efficiency are summarized from the perspectives of interfacial tension regulation, CO 2 mass transfer, oil swelling and viscosity reduction, and wettability alteration. Regarding CO 2 storage, this paper further discusses the influence of foam on CO 2 flow pathways, spatial distribution, and the contributions of different trapping mechanisms, and summarizes the roles of experimental evaluation and numerical simulation in identifying CO 2 storage mechanisms. However, under complex reservoir conditions, CO 2 foam still faces challenges such as insufficient long-term stability, limited deep propagation capacity, difficulty in quantitatively distinguishing the contributions of EOR and storage, and inadequate field-scale evaluation. Future research should focus on the development of temperature-and salinity-resistant composite foam systems, multiscale in situ characterization, long-term storage numerical simulation, and synergistic optimization of EOR and storage, thereby providing theoretical support for the field application of CO 2 foam flooding and CCUS-EOR in low-permeability and tight oil reservoirs.