The head of the energy giant "Shell" said that "a very difficult winter in Europe is on the way", in anticipation of a significant increase in energy prices.Ben van Beurden added, during an energy conference, that the rationalization of energy use in Europe cannot be ruled out, due to concerns about gas supplies from Russia.Energy prices rose earlier this year after Russia invaded Ukraine.Russia has also been accused of using gas as a "weapon" to reduce its exports in response to European Union sanctions