Impact of operational parameters on water invasion in underground hydrogen storage: A numerical investigation of the Ahuroa field, New Zealand

Underground hydrogen storage (UHS) in depleted gas reservoirs is a possible solution for large-scale seasonal energy storage. A key challenge with UHS lies in an elevated gas-water contact zone due to prior hydrocarbon exploitation. This condition increases the risk of water invasion during hydrogen injection and withdrawal operations, adversely affecting overall storage performance. However, the mechanisms controlling this phenomenon and effective mitigation strategies remain poorly understood. This study aims to optimize UHS operational strategies by investigating the impact of operational parameters on water invasion behaviour using a model based on an existing underground gas storage (UGS) facility. In this study, numerical simulations were conducted to evaluate the influence of various operational parameters, including cushion gas injection rate and volume, along with hydrogen injection and withdrawal rates, durations, and volumes. Our results demonstrate several key findings. First, hydrogen's high compressibility reduces water invasion effects compared to natural gas when injecting and withdrawing equivalent volumes. Second, extending the duration of withdrawal stage and increasing withdrawal rate significantly increases water production rate. Third, cushion gas volume strongly influences reservoir pressure, with larger volumes reducing water production due to a stabilized pressure baseline. Fourth, the amount of gas injected and withdrawn in each cycle positively correlates with water production rate, while increasing injection and withdrawal frequency mitigates water invasion effects. Finally, cushion gas and hydrogen injection rates have less impact on water invasion. These findings provide a basis for optimizing UHS design parameters in depleted reservoirs by specifying injection and withdrawal schemes and cushion gas management, intending to mitigate water invasion risks. • A compositional numerical simulation of underground hydrogen storage in the Ahuroa gas field is presented using OpenGoSim. • The influence of various operational parameters on water coning is investigated. • A sensitivity analysis is conducted to evaluate the relative importance of operational parameters. • Extending the withdrawal duration exerts the greatest influence on water coning. • Practical recommendations are proposed to mitigate water coning once it occurs.