Multiscale geomechanical assessment of casing integrity during cyclic hydrogen storage in bedded salt caverns

Cyclic underground hydrogen storage in bedded salt caverns can impose long-term mechanical loading on existing well casings through pressure-induced deformation and salt creep. This study evaluates casing integrity at Brooke-1 for a proposed hydrogen-storage cavern in the Carribuddy Formation (Mallowa Salt), at approximately 1 km depth. A sequential multiscale geomechanical workflow transfers displacement histories from a 3D field-scale hydromechanical model to a high-resolution near-wellbore finite-element model of the casing–cement–formation system. The response is evaluated over 30 years of annual injection–withdrawal cycles between 2500 and 5000 psi (17.2–34.5 MPa). The strongest casing loading occurs adjacent to thick salt layers immediately above the cavern roof, where localized S-shaped deflection and residual plastic deformation develop. The installed J-55 casing reaches local stresses approaching its yield strength. A 30-year comparison shows that L-80 reduces maximum equivalent plastic strain by approximately 22–55% at the representative critical locations while sustaining higher elastic stress. Fatigue reassessment using signed local strain histories, critical-direction projection, rainflow counting, strain-life relationships, and Miner's rule gives cumulative damage several orders of magnitude below the conventional failure criterion for both grades. Pressure-sensitivity analysis shows that the lowest median spatial-P95 casing stresses occur at the 3500–4000 psi (24.1–27.6 MPa) pressure states within the investigated cyclic schedule. Overall, localized plastic and residual deformation represent more important mechanical concerns than classical strain-life fatigue.