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Pressure Prediction in a Complex Setting Based on Field Data and Geomechanical Modeling: Mad Dog Field, Gulf of Mexico


We apply a new pressure prediction workflow that integrates borehole velocity data, geomechanical modeling, and a critical state soil model. Specifically, we incorporate the effect of both mean and shear stress in the development of excess pressure. We illustrate this workflow in the deepwater Gulf of Mexico Mad Dog Field, which is associated with an allochthonous salt body. Because of loading from the salt, stresses are not uniaxial; the horizontal stresses are elevated, leading to higher mean and shear stresses. At the Green Canyon 826-1 well within Mad Dog, we develop a relationship between velocity and an equivalent effective stress in order to account for both the mean and shear stress effect on pore pressure. We obtain this equivalent effective stress using a geomechanical model of the Mad Dog Field. We then apply the calibrated velocity-stress relationship to other wells and demonstrate how our new approach improves pressure prediction in areas near salt where mean and shear stress are different than those measured from the control well. Our methodology and results show that pore pressure is driven by a combination of mean stress and shear stress, and highlight the importance of shear-induced pore pressures. Furthermore, the impact of our study extends beyond salt bodies; the methodology used and insights gained are applicable to geological environments around the world with a complex geologic history, where the stress state is not uniaxial (fault zones, anticlines, synclines, continental margins, etc.).