Fault analysis of a salt minibasin offshore Espírito Santo, SE Brazil: Implications for fluid flow, carbon and energy storage in regions dominated by salt tectonics

Abstract

High-quality 3D seismic reflection and well data are used to investigate the distribution, evolution history and significance of tectonic faulting in a salt minibasin offshore Espírito Santo, SE Brazil. Displacement-length (Dmax-L) plots, displacement-depth (D-Z) plots and structural maps are compiled to understand the growth history of distinct fault families. Interpreted structures include crestal, corridor, listric and keystone faults. Their geometry, orientation and relative distribution reveal important differences. In detail, listric faults were formed in the investigated salt withdrawal basin following a NW to WNW strike, and show multiple bright spots and pockmarks around them. The strata into which listric faults sole out have similar seismic, lithological and petrophysical characters to known Cenomanian to Turonian source rocks, which comprise shales and marls with high gamma-ray values. Low-amplitude to transparent seismic facies further indicate the presence of ductile, highly likely organic-rich shales and marls. As a result, three evolutionary stages can be identified: a) Stage 1 is characterised by the formation of NW- or WNW-striking listric faults, keystone faults and the onset of reactive diapirism; b) Stages 2 and 3 record active diapirism due to a relative increase in sediment loading, documenting the formation of many crestal, corridor and keystone faults. Importantly, normalised leakage factor analyses reveal keystone faults to be the most favourable pathways to fluid migrating in the investigated salt minibasin. Conversely, listric faults are likely to form barriers and baffles to fluid in their lower parts.