Brent crude headed for its first weekly advance this month amid speculation that escalating tension in Ukraine may disrupt supplies from Russia , the world’s biggest energy exporter. West Texas Intermediate was set for a second weekly gain after Cushing stockpiles fell. Futures were little changed in London and are up 1.1 percent this week. Ukrainian forces moved to flush separatists from their eastern holdouts as diplomats from the U.S. and U.K. vowed to punish Russia with industry-wide sanctions if this month’s presidential election is undermined. Global demand for OPEC’s crude will be stronger in the second half of 2014 than previously estimated, the International Energy Agency said yesterday. “In the run up to the elections next week the tensions will continue,” Eugen Weinberg , head of commodities research at Commerzbank AG in Frankfurt , said by e-mail. “Even after the presidential elections it’s unlikely to calm down. So […]