SiO2-Nanofluid-Enhanced Methane Displacement in Pore Networks

SiO2 nanofluids can influence methane displacement in coal porous media by altering interfacial properties and wettability. Methane displacement by 0.05–0.50 wt % SiO2 nanofluids was investigated using interfacial characterization, droplet evaporation tests, microfluidic visualization, and coal-particle packed-bed experiments across lg(Ca) = −4 to −2. The nanofluids reduced the coal-surface contact angle and gas–liquid interfacial tension by up to 22.2% and 8.74%, respectively. At low Ca, nanofluids broadened the invasion front, increased pore-network coverage, and reduced unswept regions, consistent with wettability-related changes that favored invasion of the wetting liquid. As Ca increased, the invasion patterns became more compact and laterally connected, while the concentration response differed between the regular microfluidic network and the randomly packed coal bed. Evaporation tests further revealed concentration-dependent contact-line pinning and particle enrichment on coal surfaces. Overall, methane displacement was jointly influenced by interfacial properties, capillary conditions, nanoparticle concentration, and porous-medium structure.