THE inking of a $US15.1 billion ($14.7bn) Canadian deal that could beat Chinalco's purchase of a stake in Rio Tinto as China's biggest acquisition abroad has shone a light on the Asian giant's local energy intentions.

China National Offshore Oil Corporation this week agreed to the friendly purchase of Alberta-based Nexen, trying its hand at another mammoth North American energy deal after its 2005 attempt to buy Unocal in the US for $US18.5bn fell through in the face of political opposition.

If it goes ahead, it will beat Chinalco's $US14bn 2008 acquisition of a 9 per cent stake in Rio as the biggest outbound Chinese purchase.

Nexen has a broad petroleum portfolio, both in terms of its product source -- offshore oil, oil sands, shale gas -- and its geography, operating in Europe, Canada, the US, the Middle East and Nigeria.

But the deal is being noted for the way it consolidates CNOOC's position in the lucrative Canadian oil sands sector.

 ..."The Nexen deal shows China is stepping up its level of investments in Canada -- they already have some energy interests there and now they've gone up to a much higher level," UBS analyst Gordon Ramsay said.

"Does it happen here over time? Who knows, it's a tough call. Long-dated projects with export volumes into China, such as Canadian oil sands, are appealing to them, so here in Australia you would have to say LNG possibly fits into a similar category."

The deal shows CNOOC is willing to spend big on unconventional oil and gas as it looks to secure energy, which is where things could become interesting for Australia if regulatory concerns can be overcome.

Unconventional gas, which includes coal-seam gas and shale gas, is at a much earlier stage of development in Australia than in Canada, which has been successfully tapping oil sands for years.

This could mean any big move into Australia's unconventional gas resource might not come until proven export projects were built.

China, through its three big state-owned petroleum companies, has been increasing its interests in Queensland's coal-seam gas export projects during the past three years as it looks to rapidly expand its share of overseas production.

CNOOC has a 5 per cent stake in BG Group's Queensland Curtis LNG project, Sinopec has a 25 per cent stake in the Origin Energy-ConocoPhilips Australia Pacific LNG project and PetroChina linked up with Shell in the 50-50, $5bn purchase of Arrow Energy and its coal-seam gas field in 2010.

Further illustrating its taste for non-conventional energy plays, in 2010 CNOOC agreed to earn a half share in the Galilee Basin permits of junior Exoma Energy by spending $50m on exploration across three years.

The company also has a joint venture with Altona Energy, which is listed on London's AIM exchange, to develop the Arckaringa coal-to-liquids project in South Australia.

A factor that could weigh on any Chinese moves on local companies is the trouble mining companies have run into with the Foreign Investment Review Board, most notably Chinalco in 2009 when it tried to double its stake in Rio and take stakes in its best projects, Bernstein Research has previously labelled Oil Search, Karoon, Woodside and Origin as potential targets for China, while others have suggested Santos is looking cheap at present.