* To pay ExxonMobil up to $744 mln for Scarborough gas field stake
* Scarborough has been stuck on drawing board for nearly 40 yrs
* Offshore site is remote, deep
* To raise A$2.5 bln via share offer to existing shareholders
* Share offering at 13 pct discount to last trade
* 2017 profit rises 18 pct, misses broker forecasts (Adds analyst, investor comments)
By Sonali Paul
MELBOURNE, Feb 14 (Reuters) - Woodside Petroleum WPL.AX , Australia's biggest independent gas and oil producer, launched a surprise A$2.5 billion ($1.96 billion) share sale on Wednesday to raise funds to take control of and develop a long-stranded gas field off the country's west coast.
Woodside said on Wednesday it had agreed to pay $744 million for ExxonMobil Corp's XOM.N 50-percent stake in the Scarborough field, a project that has been stuck on the drawing board for nearly 40 years due to factors including its remote, deepwater location.
The company said that soaring international demand for gas meant the time was right for the acquisition, with the field expected to feed an expansion of its Pluto liquefied natural gas (LNG) plant in the state of Western Australia.
"The difference between supply and demand is opening up very, very quickly," said Woodside Chief Executive Peter Coleman, adding that Chinese appetite for LNG was growing rapidly.
But some analysts underscored the challenges of developing the field, with Ben Wilson at Royal Bank of Canada describing the site in a broker note as "deep, distant, dirty and dry".
The move puts Woodside, seen as short on near-term growth prospects, in control of Scarborough with a 75-percent stake, working with BHP Billiton BHP.AX BLT.L on a project now estimated to cost up to $9.7 billion.
The rest of the money raised through the A$2.5 billion offer to existing shareholders will be used to support work on Scarborough, the Browse LNG project in Australia and the SNE oil development off Senegal.
Analysts said that even with the large equity raising, Woodside may have to come back to investors in a few years to fund the development of Scarborough and Browse. Woodside has a market value of A$26 billion,
"There's a lot of money to pay," said Macquarie analyst Andrew Hodge.
The company announced the Scarborough deal after reporting an 18-percent rise in annual profit of $1.02 billion, just short of analyst forecasts.
Woodside's shares were on a trading halt for the offering, which closes on Thursday. It is offering one new share for every nine shares owned at A$27 a share, a 13-percent discount to Woodside's last trade.
GAS UP?
The company also said it was pushing out a final investment decision on the Browse LNG project off Western Australia to 2021, a year later than last flagged and now estimated to cost $15 billion to get to start-up.
"A lot of Woodside capital is due to be chewed up in coming years with the Senegal, Scarborough and Browse developments," said Saul Kavonic, an analyst at consultants Wood Mackenzie.
"All face uncertainties and risk delays ... but Scarborough could now prove the most 'do-able' of the three."
BHP Billiton BHP.AX BLT.L welcomed Woodside's expanded role in Scarborough.
"This development could enhance the commercial viability of Scarborough and the region," BHP's petroleum president Steve Pastor said in a comment emailed to Reuters.
Part of the $744 million cost of the stake in Scarborough will only be due when the project, in 900 metres of water with no liquids to boost the value of the gas, gets its final go-ahead.
"Exxon (NYSE:XOM) aren't in the habit of making dumb decisions. They probably see more future in Qatar, PNG (Papua New Guinea), Mozambique and Golden Pass (in Texas)," said Andrew Blakely, an analyst at fund manager Perpetual.
Meanwhile, Woodside on Wednesday said the North West Shelf LNG joint venture is pursuing arbitration on an LNG contract dispute with Korea Gas Corp (KOGAS).