The Sealing Failure Mechanism of Old Well Plugging Section under Thermo-Mechanical Coupling in Salt Cavern Hydrogen Storage

To address the plugged sections of old wells in salt-cavern hydrogen storage facilities, this study establishes a three-dimensional finite element model considering fluid-solid-thermal multi-field coupling effect is established. based on the Cohesive Zone Model (CZM). The model simulates the debonding failure process at the cement plug-formation interface and investigates the effects of various gas injection scenarios, operational pressures, formation temperatures, mechanical parameters of the cement plug, and interface bonding quality on the debonding failure length. Simulation results indicate that hydrogen, compared to natural gas, is more prone to interface debonding failure and leakage. Increasing the cement plug’s elastic modulus from 5 to 15 GPa reduces the debonding failure length by 10.37 m and increases the fracture propagation pressure by 2.2 MPa, demonstrating that higher elastic modulus effectively mitigates the risk of interface bonding failure. Increasing the Poisson’s ratio from 0.05 to 0.20 only reduces the debonding failure length by 2.2 m and increases the fracture propagation pressure by 1.2 MPa, indicating that Poisson’s ratio has minimal impact on bonding failure. Micro-annular gaps are highly sensitive to bonding quality, highlighting the need for rigorous quality control at the bonding interface. Under constant low operating pressure, minor debonding persists at the interface, but as operating pressure increases, the debonding failure length grows rapidly. Additionally, with increasing temperature, the debonding failure length gradually decreases. The research findings provide guidance for the optimization of cement slurry formulations and the underground hydrogen storage process.OPEN ACCESS Received: 07/04/2025 Accepted: 10/06/2025