西沙周缘深水沉积盆地演化及油气勘探潜力

Basin Evolution and Petroleum Prospecting Potential of Deepwater Sedimentary Basins around Xisha Islands

西沙周缘深水沉积盆地位于南海西北部深水区,属新生代盆地,主要经历了三次构造运动和断陷与坳陷两个演化阶段。西沙北坳陷带和中建坳陷沉积了厚层的断陷期和坳陷期地层,断陷早期发育烃源岩,断陷晚期发育主要储层;坳陷早期发育储层,坳陷晚期发育区域盖层,具备优越的生储盖条件。西沙南坳陷带构造运动强烈,地温梯度高,局部出现洋壳基底,坳陷发育时代较晚。推测西沙周缘沉积盆地成藏模式与莺歌海盆地类似,中中新统海相泥岩具有生烃潜力,深水水道砂体可作为储层,海相泥岩为区域盖层。通过分析各个盆地(坳陷)的生储盖特征,认为西沙周缘具有优越的油气地质条件,是进行油气勘探的有利区域。

The Cenozoic sedimentary basins around Xisha Islands distribute in the deep water region in the northwest part of South China Sea. Three tectonic movements and two tectonic evolutions, one rift-faulting and one depression, have been undergone in this region since Cenozoic era. As a result, a large thickness of Cenozoic sediments deposited in the North Depression Belt and Zhongjian Depression. Source rock and reservoirs mainly formed respectively during the early and the late rift-faulting stages while reservoirs and regional cover formed respectively during the early and the late depression stages. It is deemed that there are excellent source-reservoir-caprock conditions where. In South Depression Belt, affected by intensive tectonic movements and accompanying high geothermal gradient, the ocean crust basement occurred in local and so depressions developed late. It is deduced that the hydrocarbon accumulation model of these peripheral basins is probably similar with that of Yingehai Basin, in which the marine middle Miocene mud- stone is of good hydrocarbon-generating potential and the deep-water channel sandstone can be severed as reservoirs with marine mudstone acted as the regional cover. By analysis of the characteristics of hydrocarbon plays in every basins or depression, it is concluded that abundant hydrocarbon resource exists in the Xisha Islands region which is sig- nificant for exploration.