Frontier Exploration off the Continental Shelf of the Great Australia Bight: Early Delivery of an Integrated Regional Seabed and Shallow Overburden Model for Conceptual Well Planning

Abstract

BP was awarded acreage in the Ceduna Sub-Basin, Great Australian Bight, South Australia in 2011. The relatively unexplored, deep water and geologically complex setting required BP and Partners to adopt an integrated, front end loaded, approach to support conceptual well planning. Upon entry, access to quality government databases helped establish a solid foundation of understanding, with new offshore programs used to build on this. Key to this was 12,000km² 3D seismic, acquired by BP in 2011. The 3D seismic volume imaged deep exploration targets under a rugose, dipping seabed and a complex faulted overburden. A sub-set of the 3D data was re-processed to maximise spatial and vertical resolution for shallow geohazards mapping in the top-hole section. The “Geohazards” 3D volume allowed a regional ground model to be developed. The geomorphological model developed understanding of a one-time dynamic seabed with features including canyon and channel systems, building on work by Heap and Harris (2008), as well as near-seabed slope failure across the area. The geotechnical model aided the understanding of seabed soil variability and potential shallow drilling constraints. Ground truthing the results was an important part of the model building process. A reconnaissance site investigation program was performed in 2013 and focused calibrating the geotechnical, environmental and geochemical nature of the seabed soils. Sampling techniques included piezo-cone tests, cores, and water column sampling, all correlated using echo-sounder and sub-bottom profiler data. Radiocarbon age dating was undertaken on key cores to understand the relative age and sedimentation rate across the seabed. The seabed was dated to be c.7000 years old, with a present sedimentation rate of no more than 33m/m.y. This information has helped shed light on the likely inactivity of the slope failure. The approach followed has produced a regional seabed and shallow overburden model for well planning to support early conceptual well planning and allow this to be considered in the well location selection process. It demonstrates that integration of old and new datasets is vital in developing a robust ground model. Early commitment of a multi-disciplinary team, from the bid stage, was key to the successful strategy implementation.

AAPG Datapages/Search and Discovery Article #90217 © 2015 International Conference & Exhibition, Melbourne, Australia, September 13-16, 2015