“源热共控”中国海油气田“近岸油、远岸气”有序分布

“Co-Control of Source Rock and Heat” in Orderly Distribution of “Near-shore Oil and Far-shore Gas” in China's Offshore and Adjacent Area

中国海及邻区自中生代末以来经历5期成盆,形成多个新生代盆地。该区烃源岩形成期分古新世、始新世、渐新世和中新世4期。烃源岩类型有陆相、海陆过渡相和海相,其中陆相有半深湖相、湖沼相泥岩;海陆过渡相包括煤系三角洲与浅海相,主要为煤层、碳质泥岩和暗色泥岩;海相分陆源海相和海源海相。中国东部海域、南海北部海域和南海西部海域均具有近岸带以陆相半深湖相烃源岩为主、远岸带以海陆过渡相—海相烃源岩为主的特征;南海南部近岸带和远岸带都是海陆过渡相—海相烃源岩。中国海及邻区大地热流具有自近岸带向远岸带增高的趋势,烃源岩上覆层有自近岸带向远岸带增厚的趋势。因源热耦合作用,中国海及邻区形成以生油为主的近岸带和以生气为主的远岸带。近岸带从渤海盆地,经南黄海盆地、珠江口盆地北部坳陷带、北部湾盆地、莺歌海盆地河内凹陷、中建南盆地西部、万安盆地西部、湄公盆地、曾母盆地巴林坚坳陷、文莱—沙巴盆地中南部,向东北方向延伸到巴拉望盆地东部,是巨型石油生成区,已发现石油储量上百亿吨。远岸带包括东海盆地、台西盆地、台西南盆地、珠江口盆地南部、琼东南盆地、莺歌海盆地莺中坳陷、中建南盆地东南部、万安盆地东南部、曾母盆地康西坳陷、文莱—沙巴盆地北部、巴拉望盆地西部,是巨型天然气分布区,累计发现天然气储量数万亿立方米。目前中国海主要在成熟区的构造圈闭领域、特别是中浅层构造圈闭领域和生物礁领域勘探,复合圈闭和岩性圈闭的勘探刚刚起步,勘探新层系和新类型广阔;中国海勘探新区较多,尚有一批极具资源潜力、勘探程度很低的盆地或凹陷,特别是远岸带的深水区,预测其勘探潜力巨大。

China＇s offshore and adjacent area experienced five basin-forming stages since the end of Mesozoic, leading to development of a number of Cenozoic basins. Source rocks in the region were developed in Paleocene, Eocene, Oligocene and Miocenes. Types of source rocks include nomareine, transitional, and marine facies. Source rocks of nonmarine facies refer to mudstones of semi-deep lacustrine facies and limnetic faices. Source rocks of transitional facies include coal beds, coaly mudstones and dark mudstones. Marine source rocks include terrigenous marine and pure marine facies. Source rocks in the East China Sea, northern South China Sea and western South China Sea are dominated by semi-deep lacustrine facies in near-shore area and transitional to marine facies in far-shore area. Source rocks in southern South China Sea are featured by transitional to marine facies in both near-shore and far-shore area. Geothermal flux in China＇s offshore and adjacent area increases from near-shore area to far-shore area, and formation overlying source rocks get thicker from near-shore area to far- shore area. Because of co-control of source rock and heat, the near shore is distributed mainly with oil and the far shore distributed with gas in China＇s offshore and adjacent area. The near-shore belt extends from Bohai Bay Basin via southern Yellow Sea Basin, depression belt in northern Pearl River Mouth Basin, Beibu Bay Basin, Hanoi depression of Yingge Sea Basin, western part of Zhongjiannan Basin, western part of Wan＇an Basin, Mekong Basin, Balinjian depression of Zengrnu Basin, and central and southern parts of Brnnei-Sabah Basin northeastward to eastern part of Palawan Basin. This is a huge oil-generating belt with billions of tons of discovered oil reserves. The far-shore belt includes East China Sea Basin, Taixi Basin, Taixinan Basin, southern part of Pearl River Mouth Basin, Qiongdongnan Basin, Yingzhong depression of Yingge Sea Basin, southeastern part of Zhongjiannan Basin, southeastern part of Wan＇an Basin, Kangxi depression of Zengmu Basin, northern part of Brunei-Sabah Basin, and northern Palawan Basin. This is a huge natural gas generating belt with the discovered natural gas reserves accumulated to trillions of cubic meters. Currently, China＇s offshore area is located mainly in the structural trap domains of the mature zones, the structural trap domains of the middle and shallow layers and biological reefs in particular. Exploration of compound traps and lithologie traps is under the preliminary stage. There is a broad prospect for exploration of new series of strata and new types. There are a lot of new exploration area in China＇s offshore area. A number of basins and depressions with great potential for resources are at low degree of exploration. The deepwater zone of the far-shore belt, in particular, is predicted to have a great potential for exploration.