JAMES, SIMON, JOAN HORBEEK, and TOR TAKLO, A/S Norske Shell & Eamonn Doyle Geopressure Systems Inc.

Abstract: Optimising Well Casing Design In A Frontier Deepwater Basin Using Real Time Pore Pressure Prediction Whilst Drilling

During 1998 Norske Shell drilled the first well in the Vøring Basin. The well design had to be flexible to accommodate considerable uncertainty in the lithological, age and pore pressure prognosis due to lack of nearby offset well control. The pore pressure prediction was an integrated team effort with important input from the drillers, mudloggers, mud engineers, LWD engineer and operations geologist/geophysicist. At the rig site a pore pressure engineer integrated all possible pressure indicators (LWD resistivity and sonic logs; drilling exponent; mud gas levels; drilling parameters) in real-time. Crucially the process was documented in a casing setting depth decision tree showing well programme scenarios in different pressure regimes, seismic calibration, critical responsibilities and information flow. The well was drilled on time and within budget despite slow ROP?s and losing 9 days when respudding due to shallow water flow.The main contributor to the good cost performance was the ability to drop casing strings and to set others deeper in response to the real-time pore pressure prediction which indicated only mild overpressures.The total cost saving was in the order of 7 million USD. No direct pressure measurements could be taken in the well due to poor reservoir development so that the pore pressure prediction made largely in claystones remains uncalibrated. It is a measure of the belief built up in the pressure prediction techniques through good planning and full involvement of a multidisciplinary offshore team in the prediction that such cost savings could be made.

AAPG Search and Discovery Article #90923@1999 International Conference and Exhibition, Birmingham, England