Royal Dutch Shell and the China National Petroleum Corp (CNPC) have signed a deal to boost cooperation in sectors like deep sea exploration as well as liquefied natural gas (LNG) and unconventional gas sources like shale, CNPC said on Wednesday. The two companies had agreed to join forces in the development of both upstream and downstream energy businesses, CNPC said on its website. Ben van Beurden, in his first overseas visit since becoming Shell's chief executive, told CNPC Chairman Zhou Jiping that both sides have set up deep and wide-ranging ties and have huge room for further cooperation. The Anglo-Dutch firm is already one of the biggest overseas investors in China's energy sector…