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Seismic Pore Pressure Prediction Enhanced with Geomechanical Modeling

Abstract

We present a workflow that uses geomechanical modeling to enhance the predrill prediction of pore pressure and stresses from seismic velocity. Standard, vertical stress methods assume that pore pressure depends only on vertical stress, but experimental data show that pore pressure in mudrocks depends on mean and shear stress, which can vary significantly across complex geologic formations. We calculate pore pressure as the difference between total and Previous HiteffectiveNext Hit mean stress. We estimate total mean and shear stress from geomechanical modeling of the formation, and the Previous HiteffectiveNext Hit mean stress from velocity by using a relation derived between velocity, and Previous HiteffectiveTop mean and shear stress. We demonstrate our workflow by predicting pore pressure and full stress field around a salt body in the Mad Dog Field, Gulf of Mexico. and use it to p Geomechanical modeling of the salt system predicts that salt outward push increases mean and shear stress in sediments adjacent to the sides of the salt body. Therefore, our workflow predicts that pore pressure in these sediments is higher and minimum stress is lower than predicted by standard, vertical methods, predicting narrower safe mudweight window ahead of the drill bit. In addition to improving wellbore design, our enhancement of pore pressure and stress prediction also helps better understand hydrocarbon migration and trapping across a formation, and better estimate the sealing capacity of caprocks and hydrocarbon columns.