The impairments are largely related to its PNG exploration licences.
As part of the company's ongoing strategic review a number of exploration and evaluation assets in PNG have been identified as being reduced priority due to lower prosperity or sub-optimal economics.
The company said there was no intention to pursue activities on these assets and as such, the full value of these exploration assets would be written down.
The expected impairment expense is a non-cash item and will not impact cash earnings or cashflow.
Shares in Oil Search (ASX:OSH) are tracking 1 per cent higher at $3.03.