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Petroleum Systems and Exploration Potential of the Offshore China Basins

Belopolsky, Andrei 1
1 BP, Sunbury on Thames, United Kingdom.

The petroleum systems of the Chinese basins have many similarities. The basins are largely Tertiary in age, with two main source rocks: lacustrine shales and alluvial plain or transported coals. Oil-prone lacustrine shales are found mainly in some of the rifts grabens on the shelves. Bohai Basin is the most prolific Chinese offshore basin with 25 BBOE already discovered where these shales are mature.

In the outer shelf and deepwater areas, the lacustrine shales are less likely to be present, and the wide-spread coaly source rocks play the most important role. The key is to locate areas with sufficient overburden where these coals are mature. Interpretation of the gravity and magnetic data, integrated with regional 2D seismic data and reconstruction of the tectonic history, allowed us to identify areas in the East China Sea where the Tertiary back-arc basins should be turned on. Two very large rivers, Huang He and Yangtze, have been delivering vast volumes of sediments to the Yellow Sea and East China Sea and created sufficient overburden as well as deposited sandstone reservoirs. Inversion has created structures capable of trapping hydrocarbons.

In the South China Sea, most of the exploration has been concentrated on the shelf and has been largely disappointing. The deepwater areas remain underexplored. Recent deepwater Liwan 3-1 discovery in the Pearl River Mouth Basin brought these areas into the spotlight. Deepwater extensions of the Qiongdongdnan and Pearl River Mouth basins have gas exploration potential where coaly source rocks are present and mature. The reservoirs are the shallow marine sandstones and turbidites from the material brought in by the Red and Pearl Rivers. The challenge is to find substantial mature kitchens and traps with large fetch areas.

 

AAPG Search and Discovery Article #90090©2009 AAPG Annual Convention and Exhibition, Denver, Colorado, June 7-10, 2009