Macroscopic and microscopic insights into CO2-responsive viscoelastic foam for conformance control and enhanced oil recovery

Carbon dioxide (CO2) flooding is an effective enhanced oil recovery (EOR) method, yet its application is often restricted by gas channeling due to reservoir heterogeneity. To overcome the insufficient stability of conventional CO2 foams, a highly stable viscoelastic CO2-responsive foam system (DETA/SDS) was adopted. Its EOR and channeling control performance were evaluated through macroscopic physical simulations (single long and parallel sand-packed tubes) and microscopic glass-etched models. In single long sand-packed tubes, the DETA/SDS CO2 foam increased oil recovery by 37.66% relative to pure CO2 flooding, with a maximum resistance factor of 96 and a residual resistance factor of 36, outperforming N2 foam and confirming CO2 responsiveness. In parallel sand-packed tubes, the foam enhanced recovery by 35.94% and 53.16% for high- and low-permeability layers, respectively, effectively blocking the high-permeability layer while displacing oil from the low-permeability one. Microscopic visualization indicated that foam generation in porous media was dominated by rock cutting and necking separation, attributed to the high elastic modulus of the gas–liquid interface (high Wi). Notably, the foam system not only plugged dominant seepage channels via the superimposed Jamin effect but also emulsified crude oil into O/W emulsions, which further increased flow resistance and mobilized residual oil. The synergistic interplay of the Jamin effect (expanding sweep volume) and emulsification (facilitating oil detachment and transport) was identified as the core EOR mechanism, enabling effective utilization of residual oil in both mainstream lines and corner areas. This study offers a new strategy for mitigating CO2 channeling in heterogeneous reservoirs.