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Stress, Deformation and Failure Associated With Salt-Sheet Emplacement


We use evolutionary geomechanical models to study stress, deformation, and failure of basin sediments caused by the emplacement of salt sheets. We examine three case histories: a salt sheet advancing with thin roof; a sheet advancing with multiple thin layers that eventually roll over in front of the salt; and a salt sheet advancing with episodic sedimentation and shortening, involving salt inflation and roof overturn. We show that sediments develop high differential stresses as they fold in front of rolling salt sheets. In many cases, shear stress reaches the shear strength and sediments are failing. We discuss that roof sedimentation rates affect the morphology of the advancing sheet (ramps and flats) and hence lead to either frontal thrust zones or more coherent folds with lower shear stresses. Furthermore, we discuss that as the salt sheet buries sediments, their strength increases due to the imposed salt weight. Finally, we show that the salt-base geometry can provide a first order estimation of the level of shear below salt, as well as of the change in least principal stress when exiting salt. We build our large strain models in the finite element program Elfen. We model salt as solid viscoplastic and sediments as poro-elastoplastic materials. Overall, our evolutionary models provide insights into the mechanics of salt-sheet emplacement, identify potential drilling hazards and help understand stress, strain and deformation of basin sediments near salt.