Authors: Castillo, DA

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Castillo, DA 2008, 'Constraining Pore Pressure Using Observations of Wellbore Breakouts in Shales — Case Studies in the Papua New Guinea Fold Belt Region', in Y Potvin, J Carter, A Dyskin & R Jeffrey (eds), SHIRMS 2008: Proceedings of the First Southern Hemisphere International Rock Mechanics Symposium, Australian Centre for Geomechanics, Perth, pp. 633-640,

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Shale in the Moran Field and shale encountered while drilling exploration wells in the Papua New Guinea (PNG) Fold Belt region can be associated with abnormally high pore pressure regimes resulting in severe wellbore instabilities and long non-productive time periods. The use of pore pressure profiles from conventional log-based methods have shown very limited success in recreating borehole conditions and drilling experiences in wells drilled in the area, because of the tectonic deformation associated with the PNG region. By constructing a geomechanical model consistent with rock strength and drilling conditions, we were able to constrain the pore pressure and stress coupling for the Southeast Moran area and a recent exploration well in the PNG fold belt. The geomechanical model with pore pressure profile is consistent with the stress and pressure conditions needed to explain the presence and absence of wellbore breakout observations from image data and drilling experiences. Using the geomechanical model, we evaluated wellbore stability in these shale units in the Southeast Moran Field area and in a recent exploration well. The associated postmortem of these wells confirmed the accuracy of the geomechanical model, reproducing the borehole conditions seen in image logs and the pore pressure-stress coupling within the shale units.

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