Why poro-viscoplastic modeling matters for the long-term safety assessment of hydrogen storage in salt caverns

Abstract

[Abstract:] Long-term stability of salt caverns operated for underground hydrogen storage remains a critical challenge, largely driven by time-dependent creep and stress redistribution under cyclic pressurization. We present novel contributions to long-term cavern assessment by introducing a poro-viscoplastic (PVP) framework that couples creep deformation with pore-pressure diffusion to reassess cavern integrity over multi-decade operation. This work opens new ground by demonstrating that even minimal porosity and permeability — commonly overlooked in traditional viscoplastic (VP) analyses — can significantly modify effective stresses under cyclic operation. An axisymmetric finite-element model at representative depths compares VP and PVP predictions for long and short injection–withdrawal cycles. PVP simulations produce different safety factors in instability-prone zones, driven by transient pore-pressure dissipation and the evolution of effective confinement. Results expose mechanisms absent from VP analyses and suggest VP models overestimate safety margins based on local safety-factor thresholds. The proposed approach provides a more physically grounded basis for defining safe operating envelopes.