Visualization investigation of fluid transport in multiscale porous media for CO ₂ -EOR based on microfluidic technology

During oil extraction, the recovery rates of traditional methods have been gradually declining. CO₂-enhanced oil recovery (CO₂-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 CO₂ miscible and CO₂ immiscible flooding processes. The experiments demonstrated that the cross-scale effect facilitates the rapid achievement of a 100% recovery rate during CO₂ miscible flooding, but exacerbates gas channeling during CO₂ 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 CO₂ miscible flooding, as well as the overall recovery rate during CO₂ immiscible flooding. This study enhances the understanding of multiphase mass transfer in reservoir conditions and provides critical insights for optimizing CO₂-EOR strategies, ultimately contributing to more efficient oil recovery and supporting sustainable practices in the energy sector.