Pore-Network Topology Impact on CO ₂ Sequestration via Capillary-Connectivity Mechanism

Geological carbon storage is a promising approach for long-term CO2 sequestration, yet the intrinsic link between the porous media structure and sequestration efficiency remains unclear. Previous studies have mainly characterized pore–scale geometry, but a focused investigation into how pore–network topology, specifically coordination number and pore–throat ratio, governs displacement and trapping is still lacking. To address this gap, four pore–network structures were systematically designed by varying coordination number and pore–throat ratio, and two-phase microfluidic experiments were conducted to simulate the CO2 injection and brine reimbibition process. The results reveal the “capillary–connectivity–sequestration” interplay mechanism. The capillary fingering (CF)-transition point is highly sensitive to pore–network topology, fundamentally governed by the balance between local capillary forces and network connectivity. In contrast, viscous fingering (VF) regime's control remains relatively stable. In addition, the CF-transition point, defined as the “sweet spot”, marks the optimal synergy between capillarity and connectivity, maximizing both initial and residual CO2 saturation. Specifically, structures with high connectivity and low pore–throat ratio achieve higher saturation at lower injection rates; this combination ensures both injection efficiency and security.