Halite Precipitation Dynamics Driven by Refluxing Deep Hypersaline Brines: Insights from the Permian Castile Formation (Delaware Basin, USA)

The energy transition revived the interest in evaporitic sequences to develop sites for hydrogen storage via human-made salt caverns, traditionally used to store multiple fluids, gases, and wastes. However, the complexities of hydrogen storage require an in-depth understanding of these sequences due to their heterogeneity and halite-bearing intervals containing impurities that can compromise cavern stability and trigger adverse chemical reactions.

We characterized a 1200-m-thick evaporitic sequence containing the juxtaposed bedded-salt formations of the Castile and Salado formations in the Permian Basin of West Texas and New Mexico. The Castile Formation is a mega-sulfate, where the marginal sulfate platforms’ growth controlled the halite deposition under deep-water conditions. In contrast, the overlying Salado Formation is a shallow-water mega-halite, seemingly more suitable for salt cavern development due to its thick and extensive halite accumulation. However, core description, supported by 120 XRD, 40 petrographic thin-sections, fluid inclusions, 30 ICP-AES, and 15 SEM-EDS analyses, suggest that the halite of the Salado Fm is mineralogically complex containing impurities associated with the progradation of terrigenous material from the surrounding mudflats during drawdown periods. In contrast, the deep-water halite of the Castile Fm is purer and rarely contains detrital material. Despite their lithofacies, mineralogy, and textural differences, both formations exhibit well-organized, highly hierarchical, and predictive schemes.

In conclusion, this work updates the current knowledge of sedimentological processes in deep- and shallow-water evaporitic sequences, assisting in subsurface predictions in the Permian Basin and other basins where core data is limited, such as in the Permian Zechstein Basin.