渤海海域庙西凹陷古近纪沙三段沉积期原盆面貌恢复

Restoration of the Original Sedimentary Extent of Miaoxi Sag in Bohai Sea during the Sedimentary Period of the Third Member of Shahejie Formation in Paleogene

庙西凹陷位于渤海湾盆地渤中坳陷的东南部,是渤海海域近期勘探的热点地区和潜在富烃凹陷之一。由于该地区处于郯庐断裂带穿越部位,新生代以来构造改造较为强烈,致使对其主要生烃层段古近纪沙三段沉积期的原始面貌认识不清,从而给油气勘探和资源潜力评价造成困难。本文遵循改造型盆地的研究思路,在70余条地震剖面、多口钻井资料以及样品裂变径迹分析等基础上,恢复了该凹陷沙三段沉积期的原始面貌。研究表明,庙西凹陷东部在始新世末及其后遭受过较强烈的剥蚀改造,造成凹陷东部约1/4的原始沉积地层剥蚀无存;庙西北凸起和南凸起为沙三期同沉积断块,在沙三段沉积期向庙西凹陷提供物源;庙西凹陷西北部与渤东凹陷相通,西南部与黄河口、莱州湾凹陷连通。从沙三段烃源岩的原始沉积规模和勘探实践看,该凹陷具有良好的资源潜力。

Miaoxi Sag which located in the southeastern Bozhong depression in Bohai Bay Basin, is a hot area for hydrocarbon exploration in Bohai Sea area and has recently been proved to be a potential petroliferous sag. Tanlu fault belt passing through the area has resulted in strong structural transformation since Cenozoic, which changed the original appearance of Miaoxi Sag in the sedimentary period of the third member of Shahejie Formation which is the major hydrocarbon generating interval. Therefore, it made it difficult to evaluate oil resources in this area. Employing the research thought for reformed basins, based on more than 70 seismic sections, several well loggings and fission track data, the original sedimentary extent of the Miaoxi sag during the sedimentary period of the third member of Shahejie Formation is restored in this paper. The study shows that Miaoxi Sag had been strongly reformed since the end of the Eocene epoch, nearly one quarter of the third member of Shahejie Formation were denudated on the east of the sag. The Northern Miaoxi Rise and the Southern Miaoxi Rise were synsedimentary faulted blocks, which played the role of the provenance area for Miaoxi Sag in the sedimentary period of the third member of Shahejie Formation. It was connected with Bodong Sag on the central and north of Miaoxi Sag, and bordered on Huanghekou and Laizhouwan Sag to the south of the sag. Considering the original sedimentary extent of the hydrocarbon source rock in the third member of Shahejie Formation and current exploration practices, the hydrocarbon potential resources in this sag should be enormours.