The block covers 1,922 sq km in 40-90 m of water.
Eni said the contract provides for a 6.5-year exploration period in three phases.
In its 2012 notification of blocks available, CNOOC described the area as on the southeastern slope of the Yinggehai basin and western Yabei sag of the Qiongdongnan basin.
It said the block had 5,123 line-km of 2D seismic coverage. Past drilling of six wells on the block had yielded oil and gas discoveries, according to CNOOC.