Stress and Deformation in Plastic Mudrocks Overturning in Front of Advancing Salt Sheets; Implications for System Kinematics and Drilling

Abstract

We use evolutionary poromechanical models to study stress and deformation in sediments that are deposited above a salt sheet, then are upturned in front of salt and eventually buried below salt. Sediments in our model represent rocks that are able to deform plastically. We find that high differential stresses develop, leading to shear failure of sediments as they are upturned in front of salt. However, we show that strength and failure evolve together with the salt system because the mode of loading from the advancing salt changes as sediments fold below salt. We also show that the path of salt flow is affected by the continuous changes in sediment strength. We discuss how the present-day geometry of the salt base may provide evidence of the level of shear below salt. We show that our forward modeling approach can help evaluate mechanical trap integrity by identifying areas that experienced elevated shear during earlier stages of the evolutionary process. Overall, our poromechanical models allow us to correlate kinematics of salt emplacement with the stress history of sediments and identify potential drilling hazards.