(Adds background, details on impairment)
Feb 8 (Reuters) - Australia’s top power and gas retailer Origin Energy said on Thursday it expects to book a post-tax impairment charge of A$533 million ($416.7 million) for its half year results, due next week.
The aggregate charge includes a non-cash writedown of A$360 million for its Ironbark gas field, due to a downgrade in Ironbark reserves and a revised development plan, the company said in a statement.
Post impairment, Origin expects the carrying value of Ironbark gas field development to be A$279 million.
Origin also expects to book a post-tax impairment charge of A$173 million, as a result of recognising Lattice Energy earnings from July 1 2017 up to the Jan. 31 2018 completion date.
The sale of its conventional upstream oil and gas business, Lattice Energy was completed on January 31.
The impairments follow a year of hefty writedowns, mostly on its Australia Pacific LNG project, reflecting weaker oil prices, exchange rates and costs.
The company said the aggregate impairment charge would have no impact on the full-year underlying core earnings.
Origin Energy’s half year financial results are due on February 15.
$1 = 1.2791 Australian dollars Reporting by Sandhya Sampath in Bengaluru; Editing by Toby Chopra