Seal failure and fluid flow in salt-bearing sedimentary basins: A critical example from the Espírito Santo basin, SE Brazil

Abstract

Salt giants are viewed as competent seals for sub-salt fluids. Yet, salt can reveal large inter-crystalline and polyhedral permeability when deeply buried and a certain fluid pressure threshold is reached. This work uses high-resolution three-dimensional (3D) seismic data to explain the processes favouring fluid flow in areas affected by salt tectonics, with emphasis on deformed salt structures offshore Espírito Santo (SE Brazil). Documented fluid flow features include pockmarks, dissolution related pockmarks on the crest of salt structures, gas chimneys, bright spots, polygonal fault systems, and pushed-down reflections within salt structures. Offshore Espírito Santo, fluid was sourced: a) from sub-salt compartments, b) through hydrite dewatering processes, c) through slabs in salt-withdraw basins, d) from deformed strata within salt structures, and e) from supra-salt fluids that migrated through the flanks of salt structures. Focused fluid flow on the crests of salt giants may evolve to active salt intrusion when overburden rocks are <1200 m thick, depending on the intensity of regional halokinesis. The crests of salt structures are also important fluid flow paths, particularly when developing closely-spaced fault families. As a corollary, the interpreted data show that salt dissolution and intra-salt deformation are important processes accompanying the migration of fluid into faulted supra-salt strata or evolving into active diapirism. Our study has important implications to understand salt seal breaching mechanisms around the globe.