南海北部新生代沉积演变及其油气地质意义

Cenozoic sedimentary evolution and its geological significance for hydrocarbon exploration in the northern South China Sea

南海北部新生代海陆变迁过程对北部陆缘沉积盆地的沉积充填方式及油气地质特征具有重要的控制作用。基于最新大洋钻探研究成果,结合盆地内已有资料,研究南海北部海相沉积的形成过程,探讨其油气地质意义,可为未来油气资源勘探开发提供依据。受南海洋盆扩张过程的控制,南海北部盆地新生代接受海侵过程总体表现为东早西晚、南早北晚的特点。初始海侵发生在南海东部的台西南盆地始新世,而南海西部的莺歌海盆地则发生在晚渐新世。IODP367/368航次揭示,南海盆地初始海侵期发生在约34 Ma,为南海洋盆初始打开时期;大规模海侵引起的沉积环境剧变期对应于南海西南次海盆打开的时期(约23 Ma),是南海扩张的鼎盛时期。海陆变迁过程控制了海陆过渡相、海相烃源岩及储层在盆地中的分布,南海北部各盆地海相烃源岩层系具有由东向西逐步变年轻的规律,与区域内由东向西逐步接受海侵的方向相一致。区域海平面变化受到南海海盆扩张过程及全球海平面变化的综合影响,使南海碳酸盐岩台地的发育时间也存在东早西晚、南早北晚的特点,构成南海北部自生自储式的油气藏类型。海陆变迁控制了不同盆地的沉积充填方式,奠定了海相沉积的油气资源物质基础。南海北部生储盖组合在横向上受控于物源供给及海陆变迁造成的沉积环境演变,纵向上主要受控于南海构造演化及区域海平面升降。

During the Cenozoic,sea-land transition processes have important controlling effect on the depositional and petroleum geological characteristics of the northern South China Sea sedimentary basins. Based on the latest research results of IODP and the existing data in the basin,researches about the formation process of marine sediments in the northern South China Sea are carried out,and its geological significance for hydrocarbon exploration is carried out,in order to provide a basis for the future exploration and development of oil and gas resources. With the seafloor expansion process,the northern South China Sea correspondingly showed a westward and southward marine transgression during the Cenozoic. In Eocene,marine transgression firstly occurred in the Taixinan Basin in the eastern South China Sea. Later it was not until Late Oligocene that marine transgression occurred in the Yinggehai Basin of the western South China Sea. IODP 367/368 site revealed that the initial marine transgression occurred at ca. 34 Ma,and coincided with the start of the South China sea seafloor spreading.The southwest sub-basin of the South China Sea was originally formed at ca. 23 Ma,and large-scale transgression with drastic sedimentary environment changes took place during this time. Marine source rock strata in the northern South China Sea basins gradually get younger from east to west,which is also consistent with the westward marine transgression processes. Under the comprehensive impacts of both South China Sea expansion and global sea level changes,carbonate platforms also evolved from east to west,and from south to north,and formed a self-generation and self-storage oil and gas reservoir pattern in the northern South China Sea. Conclusively,sea-land transition has controlled sedimentary infilling processes within different basins,which were formed as material foundation for petroleum resources. Horizontally,the northern South China Sea source-reservoir-cap assemblage was dominated by provenances and sedimentary environment evolution. Vertically,on the other hand,it was mainly controlled by regional tectonic events and sea level changes.