Coupled Pore Pressure and Wellbore Breakout Analysis in the Complex Papua New Guinea Fold Belt Region

Abstract

AbstractThe Ieru Formation and its underlying shales in the Moran Field in the Papua New Guinea (PNG) Fold Belt region are known for abnormally high pore pressure regimes and severe wellbore instabilities resulting in long non-productive times. 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, particularly in the lower Ieru Formation, 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. The geomechanical model with pore pressure profile is consistent with the stress and pressure conditions needed to explain wellbore breakout observations from image data and drilling experiences in the original vertical well and its two sidetracks. Using the geomechanical model, we evaluated wellbore stability for the Ieru and reservoir sections in an exploration well in South East Moran Field. A postmortem of the SE Moran-1X well confirmed the accuracy of the geomechanical model, reproducing the borehole conditions seen in image logs and implying the pore pressure-stress coupling is well understood in shales underlying the Ieru Formation and in the reservoir sections.