Microfluidics-based analysis of dynamic contact angles relevant for underground hydrogen storage

Underground Hydrogen Storage (UHS) is an attractive technology for large-scale (TWh) renewable energy storage. To ensure the safety and efficiency of the UHS, it is crucial to quantify the H₂ interactions with the reservoir fluids and rocks across scales, including the micro scale. This paper reports the experimental measurements of advancing and receding contact angles for different channel widths for a H₂/water system at P = 10 bar and T = 20 °C using a microfluidic chip. To analyse the characteristics of the H₂ flow in straight pore throats, the network is designed such that it holds several straight channels. More specifically, the width of the microchannels range between 50 μm and 130 μm. For the drainage experiments, H₂ is injected into a fully water saturated system, while for the imbibition tests, water is injected into a fully H₂-saturated system. For both scenarios, high-resolution images are captured starting the introduction of the new phase into the system, allowing for fully-dynamic transport analyses. For better insights, N₂/water and CO₂/water flows were also analysed and compared with H₂/water. Results indicate strong water-wet conditions with H₂/water advancing and receding contact angles of, respectively, 13°–39°, and 6°–23°. It was found that the contact angles decrease with increasing channel widths. The receding contact angle measured in the 50 μm channel agrees well with the results presented in the literature by conducting a core-flood test for a sandstone rock. Furthermore, the N₂/water and CO₂/water systems showed similar characteristics as the H₂/water system. In addition to the important characterization of the dynamic wettability, the results are also crucially important for accurate construction of pore-scale simulators.