Numerical simulation and experimental investigation of salt-diapirs

Abstract

The main focus of this thesis has been to understand the dynamics of salt-diapiric structures and the role of various parameters that govern the diapir structures with the help of Rayleigh-Taylor fluid instability. Rayleigh-Taylor instability occurs in the presence of two fluid layers with different viscosity and density. In this work, we present results from 2-D numerical simulations and laboratory model experiments to explain characteristics of salt-diapirs and its dependence on governing parameters. We in this study considered a two-layer system that contains heavier layer fluid lying over lighter fluid layer and these layers are of different thickness. For simulating this system, a code based on finite volume discretization and semi implicit method for pressure linked equations revised (SIMPLER) algorithm is used. Initial condition is a step-profile for concentration (density) with heavier fluid (representing sedimentary soil layer) laying-over lighter fluid layer (representing evaporative mineral layer) and is allowed to evolve in time due to diffusion and convection. Resulting Rayleigh-Taylor fluid instability helps in understanding characteristics of salt-diapirs on various governing parameters. We have also done experiments with similar configuration in a tank in which an initial step change in density across an interface (stable) is established using two layers of fluids with different densities and high viscosities. We used CMC (Carboxy Methyl Cellulose) to vary the viscosity of the water and sugar to increase the density. The unstable density stratification was obtained by inverting the tank. Experiments are done with different density difference and layer thickness ratios. Experimental results provide quantitative verification of the simulations.