Stress and Pore Pressure in Mudrocks Bounding Salt Systems

Abstract

We simulate the evolution of stress and pore pressure in sediments bounding salt systems. Our evolutionary geomechanical models couple deformation with sedimentation and porous fluid flow. We find that high differential stresses develop near rising diapirs and below salt. Salt emplacement induces significant excess pressures that are comparable to the weight of the salt sheet. In addition, we show that the shear-induced component of the excess pressures is significant. We also find that low effective stresses result in low strength, which enables salt growth. We model salt as a solid viscoplastic and sediments as poro-elastoplastic materials, and calibrate the consolidation properties based on experimental testing on smectite-rich mudrocks typical of those in the Gulf of Mexico. Our approach can be applied to design stable well bores and provide insight into macroscale geological processes. Overall, we show that transient evolutionary models can provide estimates of stress and pore pressure in many geologic systems where large strains, pore fluids, and sedimentation interact. We close with a discussion of the need to better understand material behavior at geologic stress and timescales.