Power and gas company Origin Energy has announced a raft of measures to raise billions of dollars to counter the impact of lower oil prices on its bottom line.

The energy firm plans to sell new shares to investors in the hope of raising $2.5 billion.

In April, the company's debt was downgraded by credit ratings agency Standard & Poor's to BBB-, just above junk status.

Origin is a major shareholder in the $25 billion Australia Pacific LNG (APLNG) project in Gladstone which will soon start production.

The company also plans to cut $2.2 billion by measures including slashing capital spending by $1 billion during the 2016 and 2017 financial years.

Origin will also cut dividend payouts to 20 cents a share during 2016 and 2017 to save $420 million in cashflow.

In addition, it plans to sell off $800 million of assets, including direct investments in wind power and infrastructure assets.

Origin has already sold New Zealand power firm Contact Energy and cut business expenses.

The company said it may have to write-down up to $150 million as it stops geothermal and international exploration.

That offsets an extra $53 million in exploration expenses in Vietnam.

Origin Energy said the measures will cut net debt to $9 billion by the end of the 2017 financial year and shore up the company's investment grade credit rating.

The company's chairman Gordon Cairns said the measures would strengthen Origin's balance sheet.

"We believe this package of initiatives is prudent in light of current market conditions and strikes a reasonable balance in the best interests of all shareholders," Mr Cairns said.

In a note today, S&P reaffirmed Origin's corporate credit rating at BBB- with a stable outlook.

"The affirmation of the ratings primarily reflects our view that the capital management measures announced by Origin will considerably strengthen the company's balance sheet in the medium term," said Standard & Poor's credit analyst Thomas Jacquot.

"In addition, following completion of the Asia-Pacific Liquefied Natural Gas (APLNG) project, the measures will provide a comfortable buffer to Origin's financial metrics in case of continuing depressed oil prices."

Origin said it expects underlying earnings before tax to be between $1.45 to $1.55 billion in 2016 based on an oil price of $US54 a barrel.

The global benchmark Brent crude price is currently at $US47.87 a barrel.

Origin said net profit could be pulled down in 2016 by up to $220 million dollars as the LNG project ramps up.

It expects before tax earnings to rise in 2017 to be up to $2.1 billion.

Origin is also predicting LNG before tax earnings will be $1.2 to $1.3 billion when both Australia Pacific LNG production trains start operating.

Origin was one of the biggest losers on the ASX 200 yesterday, plunging by 10.4 per cent, or $0.71, to $6.10.

Its shares are in a trading halt during the capital raising.