Norwegian state-controlled energy company Equinor will take a $1.8 billion impairment after downgrading estimates of recoverable reserves in the $7.7 billion Mariner heavy oil field in the UK North Sea.

Equinor said on Wednesday it is revising downwards an earlier reserves assessment of about 275 million barrels to about 180 million billion barrels.

It follows an updated seismic interpretation and experience from production of one of Mariner's two reservoirs — Maureen — which led to revisions to the reservoir model.