The oil giant Exxon Mobil has reached a deal to tap the Arctic in exchange for training Russia’s state-owned oil company Rosneft on the controversial drilling practice known as hydraulic fracturing, or fracking. The deal centers around a $3.2 billion exploration program for the Kara Sea on the Arctic Ocean and the Black Sea and an option for Rosneft to invest in Exxon drilling projects in the Gulf of Mexico and oil fields in Texas. Under the deal, Exxon will use its $41 billion purchase of the Fort Worth-based drilling company XTO Energy to share expertise on fracking technology to draw natural gas out of shale rock. Fracking has come under wide criticism for contaminating water supplies.