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南海西部大气区包括莺歌海盆地、琼东南盆地和珠江口盆地西部的珠三坳陷，是一个快速沉降的新生界沉积盆地。研究成果表明，南海西部大气区的天然气资源十分丰富，具备形成大气田和万亿立方米以上天然气区的地质条件：①巨厚的以海相和海陆过渡相或湖沼相为主的烃源岩地层，烃源岩母质类型以主要的偏腐残混和型和腐殖型干酪根为主，平均有机碳含量为０．５％￣５％；②多套烃源岩和晚期快速沉降构成自渐新世以来多源组合、多期叠加，

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??The giant gas area in western South China Sea includes the Yinggehai Basin and Qiongdongnan Basin as well as the Zhusan Depression in the west of Zhujiangkou Basin,being a rapidly subsiding Cenozoic sedimentary basin.Through studying it is shown that the giant gas area in western South China Sea is quite rich in natural gas resources,having the geological conditions of forming giant gas field and gas area with reserves of one thousand billion cubic meters.These conditions are:??the hydrocarbon source beds are mainly the marine and transition or lacustrine facies strata with a large thickness and the kerogen belongs to the humic type and combination type (leaning toward the former) in general,mean organic carbon content being 0.5%??5%;??the multiple source assemblage and multistage superposition since Oligocene and the gas source conditions of late accumulation after Pliocene have been formed because of the multiple hydrocarbon source beds and late rapid subsidence;??total thermogenic gas generating quantity is 773.73×10¹²m³,total resource extent is up to 11.76×10¹²m³ and the strengths of resources in the main deep depressions (rich in gas depressions) are mostly more than 2.0×10⁸m³/km².