NMR-Visualized Mechanisms of Nanoparticle-Stabilized Ternary CO ₂ Foam for EOR in Low-Permeability Reservoirs

CO2 flooding is an effective enhanced oil recovery (EOR) method. However, its low viscosity and high mobility often cause viscous fingering and channeling, especially in heterogeneous reservoirs. Injecting CO2 foam to control gas mobility and coning offers a promising solution. This study utilizes nuclear magnetic resonance (NMR) visualization to examine the conformance control and oil displacement performance of a nanoparticle-enhanced ternary CO2 foam system (CF-3) in low-permeability cores. The performance of CF-3 is compared with single-component foam (CF-1) and binary foam (CF-2) systems. Static foam stability was first evaluated under reservoir conditions (45 °C, 9.1 MPa), revealing CF-3′s superior stability, with a liquid drainage half-life of 81 min─significantly higher than CF-1 (44 min) and CF-2 (59 min). Rheological tests demonstrated that CF-3 exhibits the highest apparent viscosity, ranging from 783.9 to 2597.3 cP at different injection rates. NMR monitoring was conducted before and after foam injection. Water flooding mainly produced oil from large pores. However, an unstable front left substantial residual oil. Foam injection improved conformance control and reduced residual oil, with CF-3 providing the best sweep efficiency. This resulted in a substantial 35.65% incremental oil recovery after foam flooding. These findings demonstrate the significant potential of the ternary nanoparticle-enhanced CO2 foam system for EOR applications.