Leonardo Muniz Pichel

Title

The role of intra-salt heterogeneity on salt diapir architecture – a numerical modelling approach with applications for geo-storage

Abstract

Thick salt deposits occur in a wide range of sedimentary basins and are associated with large and geometrically complex structures owing to the inherent ability of salt to flow as a viscous fluid. Salt basins form major hydrocarbon provinces and are increasingly targeted for CO2/H2 storage, natural H2 exploration, and geothermal energy due to the unique physical properties of salt. Despite considerable advances in understanding salt basins and salt tectonics, there is still a significant knowledge gap on the internal geometry of salt structures and the original (pre-deformed) salt stratigraphy. We apply a novel, high-resolution numerical modelling approach simulating salt tectonics for rift and rifted margin salt. We investigate the influence of layered salt with various i) viscosities, ii) density, iii) thickness, and iv) stratigraphic arrangements on the kinematics and internal and external geometries of salt bodies for different basin geometries and base-salt relief. We include fully-scaled material properties to simulate halite, anhydrate and the very weak K-Mg salt layers, which are critical for the use of salt caverns for H2/CH4 storage. Our results show that layered salt with variable viscosities produces significant intra-salt strain partition but also major variability on the basin-scale salt kinematics and external structure. Layered salt with both viscosity and density variations produces even further complexities in the internal diapir geometries with highly convoluted folding, horizontal and vertical shearing, and preferential flow of the weaker, less-dense salt into the core of diapirs. Stronger salt layers tend to become trapped at the base of diapirs or underneath their associated minibasins. These stronger salt units can eventually flow into the diapir crest but are generally positioned away from their centre in cylindrical-shaped diapirs. The most complex and convolute intra-salt geometries occur around the diapirs’ flanks when the adjacent minibasins weld and there is an internal shift of minibasin depocentres towards the diapirs. Moreover, the initial stratigraphic position and thickness of these layers also play a major role on the overall evolution and internal architecture of deformed salt bodies. Our results can aid in the characterization of the internal structures of salt bodies and their relationship with their external geometry and basin-scale context, which are critical for the use of salt basins in the context of energy transition. They provide important insights that can help the design of salt caverns for H2/CH4 storage by identifying areas with broadly homogenous halite-rich salt, 2) avoid drilling through sheared and highly-stressed and strained intra-salt heterogeneities, and 3) constraining minibasin architecture and evolution, improving the understanding of the distribution and geometry of CO2 reservoirs.