南海西部中建南盆地油气地质条件和勘探前景分析

中建南盆地位于南海西部陆架—陆坡区,承接了南海北部陆坡和南沙海域构造域的地质特点,并受到南海西缘大断裂的控制,地质构造十分复杂。研究表明,中建南盆地新生代陆相、过渡相、海相各种沉积体系发育;具备有利于烃源岩发育的沼泽、泻湖、浅湖(海)—半深湖(海)、半深湖(海)—深湖(海)环境;地温梯度中—高,有利于干酪根成熟;河流、扇体、三角洲砂体和风化基岩、碳酸盐岩储层发育。受太平洋板块、印度—澳大利亚板块与欧亚板块之间相互作用产生的全球地球动力体系联合作用控制,以及南海海底扩张运动产生的区域性应力影响,盆地演化过程具有多旋回发育的特点,导致发育多套良好的生储盖组合、断裂体系和多种类型圈闭。以上各种地质要素为盆地含油气系统提供了良好的物质条件和储存空间。同时盆地具有明显油气显示。据国内外地震勘探资料,发现在盆地西北隆起带及盆地中部、南部等多处地方都有气显示,同时中国地质科学院矿产资源研究所吴必豪等在该区海底表层柱状样品中先后发现了碎块状沥青,断面新鲜,经荧光显微镜鉴定为油脂沥青,证明中建南盆地具有油气生成的潜力。因此,中建南盆地具有良好的油气远景,具备较高的油气勘探价值。

Petroleum geological conditions and prospects in the Zhongjiannan basin in the western South China Sea

The Zhongjiannan basin,located in a continental shelf-slope area of the western South China Sea,inherits the geological characteristics of the tectonic domain of the northern continental slope and Nansha sea area of the South China Sea and its development was controlled by the western South China Sea marginal fault. So the Zhongjiannan basin has very complex structure. Study indicates that: various sedimentary systems such as continental facies,transition facies and marine facies are developed in the Zhongjiannan basin; in the basin there are swampy,lagoonal,shallow lake (sea)-semi-deep lake (sea) and semi-deep lake (sea)-deep lake (sea) environments,which are favorable for the growth of source rocks; intermediate to high geothermal gradients made kerogen mature easily; the main reservoirs are fluvial,fan,deltaic sandstone and weathered bedrocks and carbonate rocks. Controlled by the combined action of the global geodynamic systems produced by the interaction of the Pacific plate,Indian-Australian plate and Eurasian plate and affected by the regional stresses produced by sea-floor spreading of the South China Sea,the basin evolution has the features of polycyclic evolution,which resulted in the formation of several good source-reservoir-cap assemblages,fault systems and many types of trap. These geological elements provide excellent material conditions and storage spaces for the petroleum-bearing system of the Zhongjiannan basin. According to seismic exploration information of China and other countries,gas shows have been found in the uplift in the northwest of the basin and many places in the central and southern parts of the basin. In addition,Wu Bihao et al. of the Chinese Academy of Geological Sciences found bitumen fragments with fresh fractured surfaces in samples from the column of the surface of the sea floor of the Zhongjiannan basin. It was identified as stearine bitumen by the fluorescence microscope. All of these prove that the Zhongjiannan basin has the potential of hydrocarbon generation. In a word,the Zhongjiannan basin has good petroleum prospects and high value for petroleum exploration.