Anglo-Dutch oil giant Shell has said it expects to be hit by an impairment of up to £1.8 billion for the year.

In a trading update on Friday, it also marginally trimmed back its forecast for quarterly oil production sales and said it has seen “marginally lower” margins in it chemicals business.

Shell did not disclose the specific cause of the impairment, although it comes after oil and gas rivals including BP and Chevron have written down billions of dollars-worth of shale assets in recent months.

The company also said its 2019 cash capital expenditure is expected to be at…