Company follows rival BP in writing down value of oil and gas fields by billions. : Oil giant Shell has warned it will slash the value of its assets by up to $22bn (£17.9bn) after the coronavirus hit demand for fossil fuels. In one of the clearest indicators yet of just how badly Covid-19 has ravaged the oil and gas industry, Britain’s largest company said it expected sales to plunge 40 per cent in the second quarter of this year due to a sharp drop in fuel prices that is expected to be prolonged.