Explorers find key to gas reserves in Australia's Otway basin

May 30, 2001
The Otway basin on and off western Victoria and southeastern South Australia, plus offshore Tasmania, has emerged as a prime exploration province with five recent discoveries. The latest, Origin Energy Ltd. group's Thylacine 1 off Victoria, may have up to 1 tcf in place.

MELBOURNE, May 30 -- The Otway basin on and off western Victoria and southeastern South Australia, plus off Tasmania, has emerged as a prime exploration province.

It now seems that explorers, aided by 3D seismic, may have found the basin's "signature." Discoveries over the last 30 years like the smaller onshore North Paaratte, Katnook, Ladbroke Grove, and offshore Minerva and La Bella fields came amid a far greater number of dry holes

Origin Energy Ltd. group's Thylacine 1 gas discovery last week is the latest in a string of Otway discoveries over the last 5 months.

Thylacine 1, on Tasmanian permit T/30P about 70 km off the Victorian coast in 100 m of water, is regarded as one of the most significant finds since the North West Shelf. Preliminary estimates are reserves in place may be more than 600 bcf and may exceed 1 tcf. The 281 m gross gas column is in the Cretaceous Waarre Sand, a highly productive reservoir that contains gas in most of the smaller fields in the region.

Origin has 30%, Woodside Petroleum Ltd. 50% and Benaris International Ltd. 20%. Woodside will operate the Thylacine development. Thylacine was plugged and the rig moved 15 km north to drill the Geographe prospect on permit Vic/P43.

The Santos Ltd. group (Santos 90% and Beach Petroleum NL 10%) has had five straight Waarre gas successes onshore Victoria since the beginning of the year, adding to the three fields it has on production.

After moving into the area several years ago Santos found gas at Penryn, Mylor, and Fenton in 1999-2000 and brought them on stream via its new Heytesbury gas facility.

This year's discoveries were McIntee in February, Tregony in March, Croft in April, and Lavers and Naylor in May. All but Tregony, on Santos's 100% owned PEP 153, were on permit 154. All are near Port Campbell and close to the original North Paaratte/Wallaby Creek/Brumby gas fields that Beach opened in 1979-80.

Naylor, with 30 m of net pay, is deemed the most significant with potential production of 10 terajoules/day.

Lakes Oil NL has interests in several permits, including 40% of onshore PEL 57 in South Australia that contains part of a prospect called McNamara Park. The prospect straddles the boundary with PEL 72, and Lakes will earn 7.5% in PEL72 by contributing to the McNamara Park 1 being drilled by Origin Energy.

Lakes has a 100% interest in offshore South Australian permit EPP24 which contains the Troas prospect. BHP Petroleum Pty. Ltd. drilled Troas in 1992 but did not test a gas flow because no pipelines were near. Lakes said reserves may be up to 600 bcf, and Troas could be commercial if planned Otway basin pipeline are built. Lakes plans to redrill Troas early in 2002.

The recent development of pipeline infrastructure between Melbourne and the western Victorian town of Warrnambool has improved opportunities for commercialization of onshore Otway gas discoveries.

There are pipeline proposals to link the new fields to markets in South Australia and Adelaide. The South Australian government has wanted a long-term gas supply that offered an option to the existing single pipeline from the Cooper basin. Six utilities proposed projects to the government to supply gas, including a connection with Timor Sea fields off northern Australia and several ideas tapping sources closer to home.

One of the latter was Duke Energy Corp.'s plan to build a $250 million, 670 km line from BHP Petroleum Pty. Ltd.'s undeveloped Minerva field off Victoria, gathering production from other Otway discoveries on the way. Duke said the line would need 30 PJ/year of demand but capacity would be 60 PJ. Duke wants commitments from South Australian customers before proceeding.

A rival plan announced earlier this month involves Australian National Power and Origin Energy, which established the South East Australia Gas Pty. Ltd. joint venture to build a 630 km, $200 million line from Port Campbell in Victoria to Adelaide.

This week ANP signed a deal to buy 270 PJ from BHP's Minerva over 10 years. Most will go to a planned 300-Mw expansion of ANP's 500-Mw, gas-fired power station at Pelican Point, near Adelaide.

The two pipeline projects (timed for completion about 2004) both won't be needed in the short term, but even one would sustain the renewed Otway basin exploration effort.