Utilising borehole data to characterise geological factors controlling salt cavern shapes: A multi-well case study from NW Switzerland with implications for solution mining and subsurface storage

In NW Switzerland, thick rock salt deposits (Middle Triassic) are exploited by solution mining and brine production. This salt is located within a unique anticline structure, which prospectivity have been investigated by numerous deep boreholes. This allowed an extensive acquisition of borehole data such as high-resolution borehole images, wire-line petrophysical logs and drill cores. The geometry of salt bodies, their structural complexity and lithological heterogeneities impact significantly the shape of salt caverns developed for the solution mining industry as well as for subsurface storage in salt caverns. Thus, this borehole data were analysed using state-of-the-art methods providing a profound reservoir characterisation and a in-depth understanding of internal geometry of the salt body, the structural complexity, the salt purity distribution along profiles as well as the determination of main controlling geological factors such as e.g. bedding, faults, shear zones, fractures, folds, deformation patterns and lithological heterogeneities. In addition, correlation of neighbouring boreholes contributed to a better understanding on regional salt tectonics, mechanical stratigraphy and the kinematic evolution of the investigated anticline.