Updating the Geomechanical Model and Calibrating Pore Pressure From 3D Seismic Using Data From the Gnu–1 Well, Dampier Sub-Basin, Australia

Abstract

Abstract A postmortem analysis of the Gnu–1 well was conducted to help understand the drilling experiences in the context of the pore pressure and stress profiles. The postmortem involved a review of the drilling experiences, the analysis of CAST image data, wireline log data and the LWD logs. This information was used to refine and verify a geomechanical model (in-situ stress, pore pressure and rock mechanical properties) in the vicinity of the Gnu–1 well. Of prime concern was the verification of the pre-drill pore pressure prediction previously undertaken using 3D seismic velocity data and offset well data. Wellbore failure and natural fracture analysis were an integral part of the postmortem. Wellbore breakouts seen in the image data allowed the pore pressure in the 8½" hole section of Gnu–1 to be constrained. Modelling using image data collected in the Athol Formation indicates that the pore pressure does not increase as rapidly as was estimated in the pre-drill study. Pore pressures in the North Rankin Formation and below were consistent with the pre-drill study. The geomechanical model was able to explain the losses seen in the Athol Formation in Gnu–1 when using the mud weights experienced by the open hole at the time of drilling.