Numerical study on hydrogen-water flow in the microfluidic model for underground hydrogen storage in aquifers

Abstract

Underground hydrogen storage allows hydrogen to be stored as an energy carrier in subsurface formations and extracted when needed, enabling effective energy management. However, the understanding of hydrogen-water flow behavior, as well as the changes in storage capacity and recovery rates during multiple injection and production cycles, remains insufficient. In this study, we conducted numerical simulations using the Level Set method based on microfluidic systems. We discussed the influence characteristics of the key variables common in subsurface problems or those that are difficult to control experimentally, including pore structure, wettability, and flow rate. The flow patterns, initial and residual hydrogen saturation, and hydrogen recovery rates during injection and production processes were analyzed. Our results indicate that, for the injection process, due to the combined effects of high injection pressure, capillary action, and residual hydrogen, the flow channels at thin throats, high wettability and low flow rates situations gradually narrow within cycles, revealing significant flow instability. Additionally, under conditions of high wettability and low flow rate, the initial saturation and recovery rate of hydrogen are relatively low and decrease significantly with each injection cycle. When the contact angle is 40°, the initial saturation drops from 50% to 20%, and the recovery rate decreases from 90% to 50%. When the flow rate is 2 mL/h, the initial saturation declines from 69% to 61%, while the recovery rate decreases from 86% to 61%. For the production process, much higher residual saturation from 10% to 24% is observed only at low flow rates (2 mL/h) due to capillary characteristics. These findings can optimize the injection and production processes, providing technical support for Underground hydrogen storage and ensuring long-term stable operation.