Enhanced oil recovery of tight oil reservoirs by active carbonated water imbibition: Underlying mechanisms and influential factors

Active carbonated water (ACW) imbibition has emerged as a promising enhanced oil recovery method. Nevertheless, the mechanism is insufficiently understood, particularly as pore-scale oil displacement characterization remains unexplored. Furthermore, the influence of key factors on ACW imbibition performance requires systematic investigation. This study employs a custom visualization imbibition apparatus combined with nuclear magnetic resonance scanning to elucidate the pore-scale oil displacement mechanisms in ACW, and subsequently to investigate the effects of key factors on its performance. The results show that water imbibition yields a low recovery of 16.18%, with higher recovery observed in mesopores and macropores. In contrast, carbonated water (CW) imbibition increases recovery by 15.01% compared to water imbibition, with the greatest improvement in micropores, though mesopores and macropores still show higher recovery. The recovery for ACW is further enhanced to 39.22%, with recoveries of 37.16%, 38.33%, and 40.47% in macropores, mesopores, and micropores, respectively. Imbibition recovery increases with surfactant concentration, albeit with diminishing increments. Specifically, recovery increases by 6.96% when surfactant concentration is increased from 0.01 to 0.10 wt. %, and by 2.38% from 0.10 to 0.20 wt. %. Recovery also improves with increased boundary openness and permeability. Notably, the all-faces-open boundary resulted in a 16.64% higher recovery than the two-ends-open condition. Higher permeability further enhances recovery, with improvements of 8.44% and 13.18% observed at 0.31 and 1.19 mD, respectively, relative to 0.08 mD. This study provides new insights into ACW imbibition and offers valuable guidance for its application in tight oil.