In the wake of the US shale oil and gas boom, attention is turning to Australia's shale assets.
Coal seam gas is in the headlines for all the wrong reasons but as the global unconventional energy boom rolls on, attention has switched to Australia's shale gas potential.
BHP Billiton signalled on Tuesday that it is looking at shale opportunities in Australia as part of an expansion of its US-focused shale footprint.
Shale oil and gas has transformed the US economy in the past five years, supercharging American manufacturing with cheap, bountiful energy supplies but in Australia the sector is in its infancy.
Coal seam gas (CSG) has been the focus, predominantly in Queensland, of Australia's foray into "unconventional" energy - so called because of the non-traditional drilling methods used.
Three giant liquified natural gas (LNG) plants under construction in the Queensland port of Gladstone will progressively come online and start shipping compressed CSG off to Asian markets from 2014, reaping billions in export revenue in years to come.
Patersons Stockbrokers oil and gas analyst Alexis Clark says most of the investment opportunities in CSG companies "have already been picked over", mostly consolidated with majors in deals such as Shell and Petrochina's $3.5 billion purchase of Arrow Energy in 2010.
"For shale it's a very different story, you've got a number of emerging players there," Mr Clark said.
Shale gas activity is concentrated in the Canning and Perth basins in Western Australia, the Cooper Basin in Queensland and the Central Australian basins and Mr Clark includes Buru Energy, Central Petroleum, Beach Energy and Norwest Energy among his picks for the sector.
Some have major partners to share exploration costs, such as Beach, which has partnered with US oil giant Chevron on its Cooper Basin reserves, and Central Petroleum, which has deals with Santos and Total.
Platypus Asset Management energy analyst Anna Kassianos says Australia's unconventional sector is immature and companies will need to prove up their underground resources with horizontal drilling before their real value becomes clear.
"It does come with risk - you would probably call it high-risk, high-reward," Ms Kassianos said.
"You've got to be mindful of what's going on."
Mr Clark cautions that infrastructure is also an issue - Australia has only a handful of the specialist drill rigs and teams needed to conduct the drilling and hydraulic fracturing needed to exploit shale gas.
Hydraulic fracturing or "fracking" comes with its own problems, with the practice having generated strident community opposition in the CSG industry and contributed to an effective halt being placed on most CSG activities in NSW.
Ms Kassianos said: "As much as NSW probably needs to access CSG, I think the scrutiny in place will make it harder in the longer term (to develop the assets)".
Fat Prophets analyst David Lennox believes the NSW CSG fields - held by such companies as Metgasco, AGL and Dart Energy - are unlikely to be exploited soon.
"We see better value in the conventional fields that we have coming on stream and the shales," he said.
Australia has around 50 years of conventional gas reserves but once coal seam and shale gas are added that number expands to more than 180 years, according to the federal government's Australian Gas Resource Assessment 2012.
BHP Billiton's interest in shale gas has led to speculation about a buy-in with an existing junior.
The company suffered a $3 billion writedown on its US shale assets in 2012, after buying into shale just before peaking gas prices slumped, and would want to get into Australia much earlier.
"I think definitely they could be an entrant," Mr Clark said.
"And that would be a ratification of the potential of Australia's resources."
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