Carbonate-Mimicking Microfluidic Platform for CO₂–Seawater–Concrete Flooding

Understanding the interplay between surface chemistry, pore geometry, and flooding fluids remains a central challenge in enhanced oil recovery research, particularly for carbonate reservoirs where wettability strongly governs multiphase flow. The recent microfluidic research published in Lab on a Chip journal explores this issue by addressing a major gap in microfluidic reservoir-on-chip systems: the difficulty of recreating realistic carbonate surface properties within optically clear devices.

“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. .”, the authors concluded. 

To confront this problem, the authors propose a microfluidic chip made microfabricated from a composite of PDMS and calcium carbonate. This material combination preserves the transparency and ease of fabrication associated with PDMS while introducing mineral characteristics essential for reproducing carbonate reservoir wettability. Through sessile droplet tests, the composite surface showed strong oil-wet behavior, with contact angles of 138.6° in deionized water and 130.9° in seawater, confirming its suitability as a carbonate-mimicking substrate. Fluorescence imaging further validated that the composite retains crude oil at the channel surface, demonstrating its affinity for oil and its relevance for studying reservoir-like interfacial behavior.

The microfluidic device was fabricated using SLA-printed molds filled with a PDMS–CaCO₃ mixture, cured, and bonded to a transparent PDMS layer. The authors designed both homogeneous and randomly structured porous microfluidic networks, each with a depth of 500 μm. The homogeneous version consisted of uniformly spaced square micropillars, while the random microfluidic network introduced irregular pore structures. For all experiments, the microfluidic chips were aged in crude oil for 12 hours to establish a stable wetting state before flooding. Fluids tested included deionized water, seawater, SDS solution, and a concrete-derived seawater formulation enriched with dissolved CO₂ and Ca²⁺.

In the homogeneous geometry, oil recovery reflected clear distinctions among the flooding fluids. DI water produced the lowest recovery at roughly 10 percent of the original oil in place. Seawater improved this to about 15 percent due to ionic effects that slightly shifted wettability. The seawater–concrete–CO₂ formulation reached about 20 percent recovery, likely supported by divalent cations and carbonate species that altered surface interactions. SDS solution performed the best at approximately 25 percent, driven by its strong interfacial tension reduction and surface-interaction mechanisms. Visual flooding sequences captured in the experiments illustrate how displacement fronts advance through the network and highlight local capillary trapping.

In the randomly structured microfluidic network, overall recovery was higher for all fluids, with SDS and the seawater–concrete–CO₂ solution achieving 39.98 percent and 30.4 percent recovery respectively. The irregular microfluidic geometry distributed flow pathways more broadly, limiting preferential channeling and improving access to isolated pores. Time-resolved images of pore-scale displacement show that SDS effectively mobilized oil through tight pore throats, while the seawater–concrete–CO₂ solution produced cleaner surfaces with reduced residual oil, even though its displacement front progressed more slowly.

The microfluidic study concludes that the PDMS–CaCO₃ platform provides a reliable way to examine pore-scale behavior in environments that more closely resemble carbonate reservoirs. The seawater–concrete–CO₂ formulation, although less effective than SDS in terms of displacement strength, demonstrates meaningful performance and offers a surfactant-free alternative worthy of further investigation. Together, the results emphasize how combining realistic surface chemistry with controlled microfluidic geometries enables deeper insight into fluid–rock interactions relevant to sustainable oil recovery strategies.

Figures are reproduced from A. Ratanpara, D. Guerrero, D. Cho, Abhishek, A. M. Nasrabadi and M. Kim, Lab Chip, 2026, Advance Article , DOI: 10.1039/D5LC00775E under a  Creative Commons Attribution 3.0 Unported Licence.

Read the original article: Carbonate reservoir surface-mimicking platform for CO2–seawater–concrete flooding

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