辽西凹陷古近纪沙三中期1 000 m极超深水的发现及其地质意义

辽西凹陷是辽河油田重要的油气产区，发育了世界上最好的烃源岩。优质烃源岩主要发育在古近系。辽西凹陷古近纪覆水深度可达1 000 m，是一个极超深水凹陷；超深水的发现主要是通过地震剖面解析古近纪齐家扇体来获得，通过解析1518和1631两条测线(结合岩芯沉积特征)获得了沙三中期扇三角洲前缘前积层的最大高度为1 000 m，并将其反演成古水深，发现辽西凹陷在古近纪沙三中期最大水深约为1 150 m，在这种极超深水的条件下发育了非常特殊的以含大量泥漂砾的砂砾重力流为主的沉积；扇三角洲前积层倾角为26°~29°；辽西凹陷古近纪的水深变化经历了一个极快速变深和缓慢变浅的演化过程，其快速沉陷是岩浆底辟热侵蚀塌陷及地表侵蚀使得盆地基底快速大幅沉降所致；辽西凹陷的极超深水在这种极端的裂谷快速沉降的动力背景下形成的，为沙三段优质烃源岩及油气藏的形成奠定了基础；辽西凹陷沙三中期与东营凹陷沙三中期极超深水的发现还揭示了渤海湾盆地沙三中期可能存在超大规模的深水或超深水坳陷，进而揭示了渤海湾盆地和黄海可能存在大范围的优质烃源岩和油气资源。

Discovery and Its Geological Significance of Ultra-water: 1 000 m in the Middle of Member 3 of Shahejie Formation During Paleogene in Liaoxi Depression,China

Liaoxi depression is an important petroleum producing area in Liaohe oilfield, in which the high-quality source rocks develop in Paleogene. Paleogene overlying water depth in Liaoxi depression is up to 1 000 m, and it is an ultra-deep water depression. The ultra-deep water is found primarily by seismic analysis of Paleogene Qijia fan; mainly through the analysis of lines 1518 and 1631 (combined with the sedimentary characteristics of drill core), the maximum height of foreset bed of fan delta front in the middle of member 3 of Paleogene Shahejie Formation is 1 000 m; through the inversion of paleo-water depth, the maximum water depth of member 3 of Paleogene Shahejie Formation in Liaoxi depression is about 1 150 m; a large number of mud gravel gravity flow dominated sedimentary boulders develop specially in the condition of ultra-deep water. The dip angles of delta foreset bed are 26°-29°. The change of Paleogene water depth in Liaoxi depression experiences a rapid deepening and a slow shallowing evolution; the magma erosion diapiric thermal subsidence and surface erosion make the basin basement rapid subsidence substantially. The ultra-deep water in Liaoxi depression, which is formed under the dynamic background of the extremely rapid subsidence of rift valley, lays the foundation for the formation of high-quality source rocks and petroleum reservoirs in member 3 of Shahejie Formation. The discovery of ultra-deep water in the middle of member 3 of Shahejie Formation in Liaoxi and Dongying depressions reveals the possible existence of a lot of depressions with deep or ultra-deep water in the middle of member 3 of Shahejie Formation in Bohai Bay Basin, and then reveals the potential of high-quality source rocks and petroleum resources in Bohai Bay Basin and Yellow Sea.