N₂ and CO₂ Nanobubble Enhanced Oil Recovery in Conglomerate Reservoirs Based on NMR Technology

Conglomerate reservoirs exhibit complex pore structures, and some well areas have low permeability, which restricts waterflooding performance. Nanobubbles, with their micro- and nanosize and ability to modify the molecular structure of water, show promising EOR potential. This study evaluated the displacement performance of N 2 nanobubbles (N 2 -NB) and CO 2 nanobubbles (CO 2 -NB) using conglomerate core samples from Xinjiang Oilfield, China. A bubble generation model was designed and used to conduct core flooding experiments and online nuclear magnetic resonance (NMR) tests, comparing the flow resistance, recovery efficiency, and microscopic sweep characteristics of the two nanobubble flooding systems. Experimental results indicated that, compared to single continuous gas flooding in water-saturated core samples, the average injection pressure difference decreased by 9.47% for CO 2 -NB flooding and 12.36% for N 2 -NB flooding, respectively. In oil displacement experiments, the recovery efficiency increased by 8.77% OOIP for CO 2 -NB flooding and 3.93% OOIP for N 2 -NB flooding compared to waterflooding. NMR T 2 spectrum analysis at the microscale revealed that CO 2 -NB flooding was more effective in displacing oil from small pores, whereas N 2 -NB flooding exhibited higher signal amplitudes (i.e., residual oil saturation) in both large and small pores due to premature channeling. This study confirmed that CO 2 -NB flooding demonstrated high potential in conglomerate reservoirs through synergistic effects of single-phase flow and supercritical state. These findings are significant for the future application of nanobubble flooding technology in enhanced oil recovery for conglomerate reservoirs.