From OhmyNews International (link):
Nigeria gave four of 17 drilling licenses to China National Petroleum Corp. (CNPC) on May 19. The deal cements an agreement made last month during a visit by Chinese President Hu Jintao.
China will explore two areas in the restive, oil-producing Niger Delta and two areas in the Chad basin, where oil is yet to be produced. In exchange for the licenses, China will invest $4 billion to build a railway system and power stations and to control a stake in the 110,000 barrel-a-day Kaduna oil refinery.
See also Nigeria to Give China Oil Rights for Investment by Reuters, and China gets Nigerian oil rights by Emmanuel Goujon