The government said it had taken the step after the failing to agree a deal with the two firms which would give it a majority stake in new ventures. President Hugo Chavez has been working to strengthen state control over oil production in the country. So far, 16 oil firms have agreed to change their operations into joint ventures with state oil firm PDVSA. US based Chevron, Royal Dutch Shell and Spain's Repsol are among the companies that signed the agreement on Friday. In an interview on state television, Minister Rafael Ramirez said the government took over the fields operated...