Numerical modeling of deformation in salt basins: Technical report

The report describes the dominant physical mechanisms and the material properties influence in the formation of natural salt deformation features within a salt basin. Numerical analysis techniques include one-dimensional, closed-form analytical solutions; one-dimensional analytical solutions employing a numerical propagator matrix technique; and a two-dimensional, finite-element, viscoplastic numerical code (MANTLE). The published works of earlier investigators were reviewed, along with conventional applications of the one-dimensional, closed-form solutions. Earlier work was extended to more complex multilayered, thin interbed systems, using a numerical propagator matrix. Nonlinear salt properties and two-dimensional mechanisms were modeled, including horizontal tectonic strain, predeposition-of-salt basement faulting, and postdeposition-of-salt basement faulting, with vertical shear stress produced in the overlying salt. The study concludes that the conventional analyses using assumed effective viscosities for salt and density-inversion mechanics are incorrect, first-order or major perturbations in a bedded salt formation require the application of shear stress to initiate the appropriate growth rate, a condition of postdeposition basement faulting is the probable mechanism to initiate such shear stress, and interbed and internal salt fabric (second-order and higher) deformation characteristics can be strongly asymmetric to the major deformation surfaces in the region of basement faulting/shear stress location. 28 refs., 70 figs., 3 tabs