渤海湾盆地古近纪超深水与极超深水沉积及油气地质意义

Identification of the Ultra Deep Water Deposition of the Bohai Bay Basin During the Paleogene and Its Significance for Oil and Gas Geology

沉积盆地古水深恢复及其演化是含油气盆地研究的重要内容之一,是烃源岩、储集层和盖层及油气成藏的控制因素之一。用地震方法解析三角洲前积层的厚度来研究水深是一个比较可靠的方法。文章采用这一方法,并结合部分测井、录井资料及岩心对渤海湾盆地北部的辽西凹陷、中部的南堡凹陷和近南部的东营凹陷沙三中期的古水深进行了研究,发现辽西凹陷在沙三中期发育了一个大型三角洲扇体,在其前缘相发育了含大量灰—深灰色撕裂泥砾的重力流沉积,并获得了辽西凹陷沙三中期最大古水深为1092 m;南堡凹陷沙三中期为一套暗色的泥页岩夹砂岩,最大古水深在552 m;东营凹陷沙三中期为一套暗色泥岩夹含暗色漂浮泥砾的粉砂岩,也为一套重力流沉积,结合史128井—牛43井地震测线的连井剖面,获得了最大古水深在681 m。这三个古水深揭示了整个渤海湾盆地在古近纪沙三中期是一个极超深水(≥500 m)的盆地,为形成大面积分布的优质烃源岩和大型含油气盆地奠定了一定的基础。

Reconstruction of paleo-water depth in sedimentary basins and its evolution is one of the key issues in the study of basin analysis. It is also one of the controls for the development of source rock, reservoir, caprock, and hydrocarbon accumulation. It is commonly effective to determine the water depth by analyzing the thickness of delta forest based on seismological methods. Using this methodology, combined with well logging, core data, we study the water depth in the northern depression of the Bohai Bay Basin during the middle Shasan period, including the Liaoxi, Nanpu and Dongying sags. Results show that fan-delta sand bodies were developed during the middle Shasan period in the Liaoxi sag. A large amount of gray-dark gray boulders of gravity flow deposits were developed in the fan delta front facies. The greatest water depth during this period was 1092 m. In the Nanpu sag, the depth is 552 m and dark mud shales intercalated with sandstones were developed. In the Dongying sag, the depth is 681 m,which was obtained combined with the analysis of seismic line crossing Shi 128 well and Niu 43 well, where dark mudstones, sandstones with floating dark mudstones of gravity flow deposits were developed. These three paleo-water depths reveal that the entire Bohai Bay Basin might be an ultra-deep basin （≥500m） during the middle Shasan period, which resulted in the formation of high quality hydrocarbon source rocks and large petroliferous basins.