Otway Basin Victoria

Otway Basin
Victoria

The Otway Basin is an onshore and offshore basin which extends approximately 500 kilometres from Cape Jaffa in South Australia to north-west Tasmania.

In Victoria, Beach’s operations in the Otway Basin involve natural gas production from the Halladale and Speculant natural gas fields, as well as the Geographe and Thylacine gas fields, with natural gas being piped and processed at the Otway Gas Plant near Port Campbell.

Once processed, the gas is sold to retailers who use it for domestic or commercial consumption in the East Coast gas market.

CONSULTATION ON BLACK WATCH

The Black Watch well construction is expected to start in 2019, depending on several factors including regulatory approvals, weather windows and availability of contractors.

The Project will run over phases with different levels of activity, vehicle movements and people on site.

To find out more about the project, read the Black Watch information sheet.

Black Watch information sheet

Extended Reach Drilling

The Halladale, Black Watch and Speculant Project uses an ‘extended reach drilling’ method. This allows for offshore natural gas reservoirs to be accessed from an onshore well site.

This proven technology is safe, efficient, has minimal environment impact, and limits the visual impact by avoiding the need for an offshore drill rig.

This method involves drilling up to 2000 metres below the surface, while using directional drilling techniques to steer the well offshore, reaching a total drilling distance of around 6.5 kilometres to the potential gas reservoirs under the seabed.

GEOLOGY OF THE OTWAY BASIN

The Otway basin was formed by multi-stage rift-sag and inversion phases. Late Jurassic to Early Cretaceous rifting resulted in the east-west trending Inner Otway Basin. Late Cretaceous rifting, culminating in continental breakup in the Maastrichtian, produced northwest-southeast trending depocentres beneath the outer shelf and slope. Multiple phases of compression in the Cretaceous-Recent resulted in inversion and wrenching of pre-existing structures.

The basin contains five major depocentres, the mainly onshore Inner Otway Basin, the offshore Morum, Nelson and Hunter Sub-basins and eastern Torquay Sub-basin. The Latest Jurassic-Early Cretaceous Otway Supergroup comprises up to 8km of continental and fluvio-lacustrine sediments that accumulated in grabens and half-grabens of the first rifting event.

Coastal-plain, deltaic and marine sediments of the Late Cretaceous Sherbrook Group are up to 5km thick. The Paleocene-middle Eocene Wangerrip Group sediments were deposited in coastal plain, deltaic and inner shelf settings and are separated from the open marine, mixed carbonates/siliciclastics of the Eocene-Miocene Nirrandra and Heytesbury groups, by a major unconformity.

The main exploration targets in the Otway Basin are the Waarre Sandstone at the base of the Sherbrook Group and sandstones of the Pretty Hill Formation and Katnook Sandstone/Windermere Sandstone Member in the Early Cretaceous section. The main source rocks occur in the Early Cretaceous section. Regional and intraformational seals exist in the Pretty Hill, Laira, Eumeralla and Flaxman formations, the Belfast, Skull Creek and Pember mudstones and mudstones and marls of the Wangerrip, Nirrandra and Heytesbury groups. Play types include faulted anticlines, large anticlinal features and tilted fault blocks.