Distribution and hydrocarbon accumulation mechanism of the giant deepwater Central Canyon gas field in Qiongdongnan Basin, northern South China Sea

Abstract

Abstract: The Qiongdongnan Basin, situated in the west part of northern South China Sea, is one of the important deepwater exploration prospects in China. This basin has tectonic-sedimentary characteristics and petroleum geology conditions different from other typical deepwater basins around the world. Initially, the cooperative exploration in this basin was carried out in a slow progress. Through continuous efforts and independent innovations, CNOOC Limited (“CNOOC”) has made great breakthroughs during the 12th Five-Year Plan by addressing the bottlenecks in relation to basin formation, hydrocarbon generation and accumulation, etc. During this period, CNOOC discovered the giant Central Canyon gas field consisting of several large-medium gas fields. Natural gas is mainly enriched in turbidite channel sandstones of the Huangliu Formation in the lower section of the canyon, and also in submarine fans of the Yinggehai Formation in the upper section. According to this study, hydrocarbon accumulation of this giant gas field attributes to following conditions: (1) the marine-terrestrial and marine source rocks of the Yacheng Formation serve as the major gas source rocks; (2) the turbidite channel sand and large-scale submarine fan reservoirs are shallowly buried, with favorable physical properties; (3) turbidite sandstones developed in multi stages constitute a large group of lithologic traps; (4) microfaults and fissures vertically connect deep source rocks and shallow traps; and (5) thick bathyal mudstone cap rock developed in late stage has good preservation conditions. In general, the natural gas reservoirs are characterized by “multiple reservoirs independently existing and vertically overlapped”, and controlled by structural-lithologic traps. There are still more prospects in the Central Canyon, suggesting huge exploration potential.

Key words: northern South China Sea, Qiongdongnan Basin, deepwater, Central Canyon, giant gas field, hydrocarbon accumulation mechanism, play

Wang Zhenfeng, Sun Zhipeng, Zhang Yingzhao, Guo Minggang, Zhu Jitian, Huang Baojia, Zhang Daojun, Jiang Rufeng, Man Xiao, Zhang Haiyang. Distribution and hydrocarbon accumulation mechanism of the giant deepwater Central Canyon gas field in Qiongdongnan Basin, northern South China Sea[J]. China Petroleum Exploration, 2016, 21(4): 54-64.

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