Abstract

Deriving global parameters for velocity-based pore pressure predictions in a complex overpressure origins regime is normally difficult and nonrobust. Applying large variations in Eaton’s exponent is an unsatisfactory work practice for velocity-based pore pressure prediction. This study investigates an alternative potential method to reduce the variation of Eaton’s exponent values in an environment of mixed disequilibrium compaction and fluid expansion overpressure mechanisms. Using 25 input wells, the fluid expansion components are estimated using velocity-vertical effective stress plot and then subtracted from the pressure measurements to obtain the disequilibrium compaction components. Eaton’s exponents are then derived only from the disequilibrium compaction components. The spatial variation of Eaton’s exponent is greatly reduced from the range of 1–5 to the range of 1–1.9 after removing the fluid expansion components from the raw overpressure data set. A constant Eaton’s exponent of 1.44 is used throughout the field to predict the disequilibrium compaction components and the fluid expansion components are predicted from gridding of the well data. The two components are combined to produce a final pore pressure prediction profile, which yields less uncertainty than the traditional Bowers method.

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