Carbonate reservoir surface-mimicking platform for CO₂-seawater-concrete flooding

Microfluidic platforms are increasingly used in enhanced oil recovery (EOR) studies due to their ability to visualize and control fluid displacement at the pore scale. While many designs successfully replicate reservoir geometries, mimicking realistic surface chemistry remains a challenge. To address this demand, we developed a microfluidic platform using polydimethylsiloxane (PDMS) mixed with calcium carbonate (CaCO₃) powder to emulate both the structure and oil-wet surface characteristics of carbonate rocks. Sessile droplet tests confirmed strong oil-wet behavior, with contact angles of 138.55° in deionized (DI) water and 130.9° in seawater on an oil-coated CaCO₃-based PDMS surface. Additionally, fluorescence microscopy verified oil retention within the composite surface, indicating its absorption capacity. Moreover, homogeneous and randomly structured porous networks were fabricated to assess flooding performance. A concrete-based carbonated seawater solution, enriched with calcium ions (Ca²⁺) and carbonate species like bicarbonate and carbonate ions, was used as a flooding fluid for EOR. In the homogeneous network, this solution achieved approximately 20% of the original oil in place (OOIP) recovery, compared to 25% OOIP with SDS. In the random network, where pore-scale heterogeneity presents greater flow resistance, oil recoveries were found to be 30.4% of OOIP and 39.98% of OOIP, respectively. These results highlight the synergistic effect of engineered surface chemistry and chemically active fluids in promoting oil displacement under varied flow conditions.