Previous Talks

Wednesday February 12, 2014

Modeling stress evolution around a rising salt dome

Maria A. Nikolinakou, UT Austin

Abstract

We model the evolution of a salt diapir during sedimentation, and study how deposition and salt movement affect stresses close to the dome. We built this axisymmetric model within the large-strain Finite Element program Elfen. We model the salt as solid visco-plastic, and the sediments as poro-elastoplastic. The salt is not kinematically prescribed, but flows because the ongoing sedimentation increases the average density within the basin, pressurizing the salt base. Our results show that stresses rotate near a salt dome, such as the maximum principal stress is perpendicular to the contact with the salt. The minimum principal stress is in the hoop direction, and drops near the salt dome, resulting in a reduced safe-mud window. The mean stress increases near the upper parts of the dome, leading to a porosity lower than predicted by the uniaxial approach for the same depth. We further compare this evolutionary approach with a static one (using Abaqus) and we show that the two approaches predict different stress paths and very different strains within the wall rocks. Specifically, we show that the evolutionary model predicts significantly higher shear stresses at the lower parts of a rising salt dome, and an order of magnitude higher horizontal strains than the static model. Overall, our results highlight that forward modeling can provide a detailed understanding of the stress history of mudrocks close to salt domes, which is critical for predicting stress, porosity and pore pressure in salt systems.

Speaker Biography

Maria A. Nikolinakou is a Civil/Geotechnical Engineer with a doctoral degree on theoretical soil mechanics from MIT. She is currently a Research Associate at BEG, UT Austin. Before joining BEG, she worked for Shell E&P on reservoir geomechanics. Her current research includes poromechanical modeling of basin sediments, geomechanical pore-pressure prediction, and numerical modeling in salt tectonics.