Geo-pressure on the Australian North West Shelf

Abstract

Zones of elevated geo-pressures have been encountered throughout the Australian North West Shelf. These represent a significant drilling hazard, and are often a challenge for field development. Geo-pressure generating mechanisms can be separated into two broad categories – stress-related (e.g. compaction disequilibrium) and fluid expansion. The shallower, shale dominated sections typically exhibit compaction disequilibrium, while the overpressures in the deeper sections typically are due to fluid expansion, hydrocarbon column effects and Lateral Pressure Transfer. A regional geo-pressure study has been carried out where overpressured zones were identified and described. In phase one 100 wells from the Carnarvon, Browse and Bonaparte Basins were analysed for both types of overpressure using traditional industry methods. In phase two compaction disequilibrium overpressure was estimated in 3D by well calibration to a high quality regional velocity model covering the entire North West Shelf. With the analysed wells providing the framework of the study, the regional 3D geo-pressure model provides very valuable insight into the spatial distribution of the pore pressures, including how they are linked to stratigraphy, and how they are connected between the wells.