Enhancing Shale Oil Recovery via CO2-Soluble Surfactant-Assisted Huff-and-Puff: Pore-Scale Mechanisms Revealed by Real-Time NMR Monitoring data

CO₂ huff-and-puff is an effective method for enhanced oil recovery in shale reservoirs, yet the stimulation effectiveness and CO₂ utilization/storage efficiency of pure CO₂ injection remain limited. In this study, systematic solubility tests were conducted under Jimsar shale reservoir conditions (91°C, 42Mpa) to screen and optimize three nonionic CO₂-soluble surfactants. The optimal surfactant with a concentration of 0.1 wt% was selected for CO₂ huff-and-puff experiments. By integrating nuclear magnetic resonance (NMR) T₂ spectrum characterization, the pore-scale mechanisms were elucidated. Experimental results demonstrate that although the surfactant only moderately reduced the CO₂/Jimsar shale oil interfacial tension from 3.26 mN/m to 1.09 mN/m, real-time LF-NMR monitoring revealed its remarkable differential effects on oil recovery from pores of varying sizes: small-pores (0.1ms