Visualization investigation of fluid transport in multiscale porous media for CO-EOR based on microfluidic technology.

During oil extraction, the recovery rates of traditional methods have been gradually declining. CO-enhanced oil recovery (CO-EOR) has been utilized since the 1960s; however, in recent years, it has garnered renewed attention due to its environmental benefits and economic advantages. However, there are few reports addressing multiphase mass transfer in micro- and nano-scale pores. This study employs microfluidic technology to simulate the pore structures of real reservoir rocks. A fracture-matrix porous medium chip with a network channel structure and a microscale porous medium chip featuring multiple pore-throat ratios were designed to investigate the effects of cross-scale interactions, network channel geometries, and the Jamin effect on fluid flow patterns and oil recovery rates during both CO miscible and CO immiscible flooding processes. The experiments demonstrated that the cross-scale effect facilitates the rapid achievement of a 100% recovery rate during CO miscible flooding, but exacerbates gas channeling during CO immiscible flooding, resulting in a decreased recovery rate. The Jamin effect becomes more pronounced with increasing pore-throat ratios, and the substantial capillary resistance generated by this effect in regions with high pore-throat ratios significantly reduces the rate of increase in recovery during CO miscible flooding, as well as the overall recovery rate during CO immiscible flooding. This study enhances the understanding of multiphase mass transfer in reservoir conditions and provides critical insights for optimizing CO-EOR strategies, ultimately contributing to more efficient oil recovery and supporting sustainable practices in the energy sector.