南海北部大陆边缘盆地油气地质特征与勘探方向

Geological characteristics and exploration objectives of hydrocarbons in the northern continental margin basin of South China Sea

南海北部大陆边缘新生代盆地都经历了早第三纪裂谷断陷阶段和晚第三纪裂后沉降阶段,但各盆地性质存在显著差异,可以分成拉分型和伸展型两大类,其中伸展型又可分成断陷型和断坳叠加型两亚类。烃源岩主要有湖相泥岩、海陆过渡相泥岩和海相泥岩。储集层包括海相砂岩、生物礁和陆相砂岩。该区生储盖组合主要包括陆生海储型、陆生陆储型和海生海储型。二级构造带包括隆(凸)起带披覆构造、凹陷陡坡断裂构造带、凹内断裂构造带、凹内底辟构造带、缓坡带以及隆起带生物礁等,各个盆地优势油气二级构造带各具特色。勘探领域包括已证实富生烃凹陷的精细勘探、新区勘探和天然气水合物勘探。南海北部地区油气分布受富生烃凹(洼)陷控制,已证实的富烃凹陷仍有很大潜力,是近期勘探的重点;高温高压地区的天然气勘探、深水区勘探是下一步储量增长的接替区。积极开辟和探索新区、新领域是中国南海地区勘探进一步发展的关键。储层的高温高压、低孔低渗,低阻油层和非烃气的识别,以及特殊地质条件下地球物理资料的采集处理是勘探中存在的主要问题。

All the Cenozoic basins on the continental margin of the northern South China Sea experienced two structural phases：Paleogene rift-fauh subsidence and Neogene post-rift subsidence. There exist evident differences among the basins,which can be divided into two types as pull-apart and extensional ones. The later can be further classified into fault-subsidence and fault-sag superimposed subtypes. Their source rocks include lacustrine shale, coastal plain swamp shale and marine shale, and the reservoirs are composed of marine sandstone, bioherm and continental sandstone. Source-reservoir-seal assemblages in this area include three different types,such as continental source-marine reservoir, continental source-continental reservoir and marine source-marine reservoir ones. Secondary structures for hydrocarbon potentials in different basins are characterized by drape and bioherm in uplift, faulted zone in the abrupt slope of sags, and faulted zone, diapire zone and gentle slope within sags. Explorations in this area are defined as precision exploration in the proven hydrocarbon rich sags, frontier exploration and gas hydrate exploration. The precision exploration in the proven hydrocarbon-rich sags aims at new traps, types and layer systems, while the frontier exploration aims at Tertiary and pre-Tertiary basins. Explorations in the northern South China Sea have an enormous potential because hydrocarbon-generative sags control hydrocarbon distributions and the proven hydrocarbon-rich sags are major targets for explorations in the near future. The natural gas exploration in high temperature and high-pressure formations and the exploration in deepwater areas are succeeding fields to increase the reserve next. It is crucial for the next progress in explorations in the South China Sea to actively open up and explore new areas and fields. Major problems remaining in current explorations are how to identify and deal with high-temperature and high-pressure reservoirs,low-porosity and low-permeability or low-resistivity oil layers as well as to collect and process geophysical data under specific geological conditions.