We use a transient, large-strain, forward geomechanical model to predict pore pressure evolution below an advancing salt sheet. We find that salt-sheet emplacement results in significant overpressures subsalt and a narrow drilling window. We show that these overpressures cause the effective stresses and hence the sediment strength to remain low beneath salt. As a result, mudrocks are failing during salt emplacement. We discuss that traditional, porosity-based workflows underpredict pressure beneath salt because they assume uniaxial conditions and do not account for shear-induced pore pressures. However, we show that shear (differential) stresses subsalt are high, and their contribution to overpressure significant. We model salt as solid viscoplastic and sediments as poro-elastoplastic materials, with consolidation properties that are based on experimental testing on mudrocks typical of the Gulf of Mexico. Overall, our transient evolutionary analysis incorporates the geologic loading history, accounts for shear-induced pore pressures and provides the complete stress tensor as well as pore pressure prediction over time.
Pore-Pressure Prediction Beneath Salt Sheets
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Nikolinakou, M. A., Heidari, M., Flemings, P. B., and M. R. Hudec. "Pore-Pressure Prediction Beneath Salt Sheets." Paper presented at the 51st U.S. Rock Mechanics/Geomechanics Symposium, San Francisco, California, USA, June 2017.
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