||In this study, we have developed a method for micromodels fabrication. Compared with the previous process, the fabrication is easier to manufacture and the equipment and materials used are less expensive. The micromodel produced has a 2.5D channel structure, and the vertical structure in the channel is not a simple plane, but a complex structure with irregularities. Compared with 2D micromodels, our micromodels can better represent real porous media and can more realistically show the fluids flow in real porous media. After bonding the plastic sheet and the double-sided tape, we use the CNC (Computer Numerical Control) milling machine to process the channel. Because of the high transparency of the material, it is easy to see the fluid flow after only dyeing the fluid. The dyeing fluid will show different color depths in different thicknesses of micromodels, which can be easily observed and analyzed in complex micro-models without the need to go through other complicated instruments.|
We made single-layer, four-layer, and eight-layer micromodels for imbibition and imbibition-drainage experiments. The imbibition experiment is to inject the wetting phase fluid (ethanol) into the model to discharge the non-wetting phase fluid (air). In the imbibition-drainage experiment, after the imbibition experiment, to inject non-wetting fluid (air) to discharge the wetting phase fluid (ethanol). Then we use "3 μl" ⁄"min" , 6 "μl" ⁄"min" , 60 "μl" ⁄"min" , 150 "μl" ⁄"min" and 300 "μl" ⁄"min" flow rates for experiment.
First, ethanol can flow into the deep pores of the channel in a thin micromodel. With the increase of the thickness of the micromodel, ethanol can only flow at the edge of the micro-model and fill the corner regions in the micromodel, so the ethanol saturation decreases. In the same thickness micromodel, when the capillary number of ethanol is small, corner flow movement dominates ethanol flow in micromodels and most of the air was trapped at narrow pore throats. After the capillary number is gradually increased, bulk meniscus movement dominates ethanol flow in micromodels, the air trapped in the dead-end pores. At the same thickness but the shape of the internal channel is changed, even if the same ethanol saturation we obtained after the imbibition experiment, the position of the air trapped in the channel is completely different. We can know that the simplification of the shape of the flow channel has a great influence on the flow state of the fluid.
|| P. Abgrall, and A. M. Gué, “Lab-on-chip technologies: making a microfluidic network and coupling it into a complete microsystem—a review,” Journal of Micromechanics and Microengineering, vol. 17, no. 5, pp. R15-R49, 2007.|
 A. Riaud, C. P. Tostado, K. Wang, and G. Luo, “A facile pressure drop measurement system and its applications to gas–liquid microflows,” Microfluidics and Nanofluidics, vol. 15, no. 5, pp. 715-724, 2013.
 K. Xu, P. Zhu, C. Huh, and M. T. Balhoff, “Microfluidic Investigation of Nanoparticles′ Role in Mobilizing Trapped Oil Droplets in Porous Media,” Langmuir, vol. 31, no. 51, pp. 13673-9, Dec 29, 2015.
 N. S. Gunda, B. Bera, N. K. Karadimitriou, S. K. Mitra, and S. M. Hassanizadeh, “Reservoir-on-a-chip (ROC): a new paradigm in reservoir engineering,” Lab Chip, vol. 11, no. 22, pp. 3785-92, Nov 21, 2011.
 M. Gouet-Kaplan, and B. Berkowitz, “Measurements of Interactions between Resident and Infiltrating Water in a Lattice Micromodel,” Vadose Zone Journal, vol. 10, no. 2, pp. 624, 2011.
 B. Berkowitz, "Interchange of Infiltrating and Resident Water in Partially Saturated Media," Transport and Reactivity of Solutions in Confined Hydrosystems, pp. 55-66: Springer, 2014.
 A. Alizadeh, M. Khishvand, M. Ioannidis, and M. Piri, “Multi-scale experimental study of carbonated water injection: an effective process for mobilization and recovery of trapped oil,” Fuel, vol. 132, pp. 219-235, 2014.
 H. Geistlinger, I. Ataei-Dadavi, and H.-J. Vogel, “Impact of Surface Roughness on Capillary Trapping Using 2D-Micromodel Visualization Experiments,” Transport in Porous Media, vol. 112, no. 1, pp. 207-227, 2016.
 M. Y. Ali, “Fabrication of microfluidic channel using micro end milling and micro electrical discharge milling,” International Journal of Mechanical and Materials Engineering, vol. 4, no. 1, pp. 93-97, 2009.
 R. D. Sochol, E. Sweet, C. C. Glick, S.-Y. Wu, C. Yang, M. Restaino, and L. Lin, “3D printed microfluidics and microelectronics,” Microelectronic Engineering, vol. 189, pp. 52-68, 2018.
 J. Gauteplass, K. Chaudhary, A. R. Kovscek, and M. A. Fernø, “Pore-level foam generation and flow for mobility control in fractured systems,” Colloids and Surfaces A: Physicochemical and Engineering Aspects, vol. 468, pp. 184-192, 2015.
 A. Anbari, H. T. Chien, S. S. Datta, W. Deng, D. A. Weitz, and J. Fan, “Microfluidic Model Porous Media: Fabrication and Applications,” Small, vol. 14, no. 18, pp. e1703575, May, 2018.
 S. A. Bou-Mikael, “Design and optimization of 2.5 dimension porous media micromodel for nanosensor flow experiments,” 2012.
 K. Xu, T. Liang, P. Zhu, P. Qi, J. Lu, C. Huh, and M. Balhoff, “A 2.5-D glass micromodel for investigation of multi-phase flow in porous media,” Lab Chip, vol. 17, no. 4, pp. 640-646, Feb 14, 2017.
 A. T. Krummel, S. S. Datta, S. Münster, and D. A. Weitz, “Visualizing multiphase flow and trapped fluid configurations in a model three-dimensional porous medium,” AIChE Journal, vol. 59, no. 3, pp. 1022-1029, 2013.
 V. Joekar-Niasar, M. Prodanović, D. Wildenschild, and S. M. Hassanizadeh, “Network model investigation of interfacial area, capillary pressure and saturation relationships in granular porous media,” Water Resources Research, vol. 46, no. 6, 2010.