--> The Crown Gas & Condensate Discovery, Browse Basin, NWS, Offshore Western Australia

International Conference & Exhibition

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The Crown Gas & Condensate Discovery, Browse Basin, NWS, Offshore Western Australia

Abstract

The Browse Basin is a gas-prone, Jurassic hydrocarbon province, located offshore, north-western Australia. The Basin was formed via several phases of extension, burial, reactivation and localised uplift. The Caswell Sub-Basin is located centrally in the Browse Basin and was a focus of early to mid-Jurassic extension, associated with the breakup of the Gondwanan supercontinent. The Caswell Sub-Basin is host to a number of large gas and condensate discoveries, including Santos' own Operated discoveries – Crown (2012) & Lasseter (2014). The Crown discovery provides a focal point for Santos' plan to aggregate a large resource base in the Caswell Sub-Basin. The Crown-1/ST-1 exploration well targeted a pronounced Late Triassic to Middle Jurassic horst block within the western Caswell Sub-Basin. Evaluation of the Jurassic sedimentary interval revealed high quality gas and condensate-bearing Early to Middle Jurassic reservoirs, conformably overlain by a thick succession of Late Jurassic marine shales. The complex geology of the Sub-basin not only leads to difficult conditions for seismic imaging and prospect evaluation, but also for safe drilling at the depths required. Shallow faulting, prograding carbonates and significant objective depths are among a number of obstacles faced for seismic imaging. Overpressure, loss zones, and high temperatures present demanding drilling conditions. As such, exploration in the region requires high quality seismic data, leading-edge seismic interpretation techniques, bespoke geo-pressure estimates and flexible well designs. Recent discoveries have added to the understanding of technical risks and prospectivity in the region. This presentation will highlight the complexities of exploring in the Caswell Sub-basin, and discuss some of the technical solutions that have enabled success. It will also cover remaining uncertainties and provide a summary of recent exploration of the area.