BEIJING - Chinese state-controlled oil company CNOOC Ltd. said Monday it is paying $2.3 billion for a 45 percent stake in a Nigerian oil field in its first major investment since its failed bid to take over Unocal Corp. last year. The deal adds to a multibillion-dollar string of foreign acquisitions by Chinese oil companies, which are aggressively pursuing energy supplies to fuel China's booming economy. The agreement, which requires approval from the Nigerian and Chinese governments, covers a deep-water area of the oil-rich Niger Delta region, CNOOC said. It said the area includes the Akpo oil field discovered in...