Fresh U.S. and EU sanctions imposed on Moscow will bring an abrupt halt to exploration of Russia's huge Arctic and shale oil reserves and complicate financing of existing Russian projects from the Caspian Sea to Iraq and Ghana. On Friday, the United States imposed sanctions on Gazprom, Gazprom Neft, Lukoil, Surgutneftegas and Rosneft, banning Western firms from supporting their activities in exploration or production from deep water, Arctic offshore or shale projects.