Pore scale models for imbibition of CO2 analogue fluids in etched micro-fluidic junctions from micro-model experiments and direct LBM flow calculations

We investigate both drainage and spontaneous imbibition processes at the pore scale using a combination of microfluidic experiments and lattice-Boltzmann (LB) flow calculations. First, we have fabricated a range of specifically designed etched micro-models to investigate the role of pore shape and throat width on fluid displacement. These designs include junctions with both equal and unequal channel widths in order to achieve a range of capillary entry pressures. All models were etched into Poly(methyl methacrylate) (PMMA) and chemically treated to create a hydrophobic surface. The displacement process is captured via a high-speed video microscope under ambient conditions. The experimental results were then directly compared with LB simulations. For the drainage experiments, we observe that the fluid displacement in the junction follows the Young-Laplace Law. For the case of spontaneous imbibition, however, the models with unequal channel widths display different displacement behaviour. Our experimental observations are confirmed in detail by Lattice Boltzmann Method (LBM) simulations, lending credibility to our observations. Instead of following Young-Laplace filling rules, we observe that the throat in closest proximity fills up first. This has potentially important consequences for calculation of residual saturation of CO2 at the core scale, which is determined by spontaneous imbibition of brine following CO2 injection. © 2013 The Authors. Published by Elsevier Ltd. Selection and/or peer-review under responsibility of GHGT