Enhancing Shale Oil Recovery via CO₂‐Soluble Surfactant‐Assisted Cyclic Gas Injection: Pore‐Scale Mechanisms Revealed by Real‐Time NMR Monitoring

CO 2 cyclic gas injection is an effective method for enhanced oil recovery in shale reservoirs, yet the stimulation effectiveness and CO 2 utilization/storage efficiency of pure CO 2 injection remain limited. In this study, systematic solubility tests were conducted under Jimsar shale reservoir conditions to screen and optimize three nonionic CO 2 ‐soluble surfactants. The optimal surfactant with a concentration of 0.1 wt% was selected for CO 2 cyclic gas injection experiments. By integrating nuclear magnetic resonance (NMR) T 2 spectrum characterization, the pore‐scale mechanisms were elucidated. Experimental results demonstrate that although the surfactant only moderately reduced the CO 2 /Jimsar shale oil interfacial tension from 3.26 to 1.09 mN/m, LF‐NMR monitoring revealed its remarkable differential effects on oil recovery from pores of varying sizes: small‐pores (0.01 ms < T 2 < 10 ms) showed a maximum recovery increase of 8.19% per cycle, while meso‐pores (10 ms < T 2 < 100 ms) achieved an 11.14% enhancement in the second cycle. Physical modeling using matrix‐fracture systems under simulated reservoir conditions confirmed that the surfactant primarily improves recovery by altering fluid distribution characteristics at the pore scale. GC/MS analysis further verified the effective production of C 20 + heavy components. This study provides novel insights into the pore‐scale displacement mechanisms of CO 2 ‐soluble surfactants in shale reservoirs, offering new perspectives for unconventional oil recovery optimization.