古湖泊水介质条件对混积岩相组合沉积的控制作用

Control effect of paleolacustrine water conditions on mixed lithofacies assemblages：A case study of the Palaeogene E， Dongying Sag， Bohai Bay Basin

刘惠民 杨怀宇 张鹏飞 韩同欣 刘鑫金

Huiming Liu Huaiyu Yang Pengfei Zhang Tongxin Han Xinjin Liu

渤海湾盆地东营凹陷古近系沙河街组三段浊积岩油藏是重要的油气增储领域，由于沉积期水体富灰特征明显，从而严重影响了地球物理预测精度及储层的品质。基于沉积水介质与富灰混积岩相组合具有一定成因联系，综合利用井孔、地震以及岩心的古生物、微量元素、粘土矿物、碳氧同位素等多种测试分析，在岩相组合划分及其水介质环境解剖基础上，综合多种方法量化恢复古湖盆水介质（盐度、水深）条件，从而探讨水介质条件对混积岩相组合的控制机理。研究表明，东营凹陷沙三段岩相组合可划分为7种，其中含灰混积类型有5种；古气候、古物源及深部流体直接控制着陆相湖盆的古水介质条件，碳酸盐含量受控于湖盆水体的盐度，富灰区主要分布于坨-胜断裂区、草北地区、中央背斜带及斜坡带地区，贫灰区主要分布于淡水物源注入区及深洼区。因此，浊积岩下一步勘探的重点方向为前三角洲附近的淡水影响区和洼陷中心的淡水稀释区。

Turbidite reservoirs in the 3 member of the Palaeogene Shahejie Formation （hereinafter referred to as E） act as an important contributor for the increase of reserves in the Dongying Sag， Bohai Bay Basin. However， their marked richness in lime in the water body during deposition， has severely affected the precision of geophysical prediction and reservoir quality. Based on the genetic link of sedimentary water conditions and mixed lithofacies assemblages rich in lime， we classify the lithofacies assemblages and depict related water conditions， as well as discuss the control mechanism of water conditions on mixed lithofacies assemblages， following the restoration of paleolacustrine water conditions （e.g. salinity， depth） via multiple means. An integration of drilling data， seismic data and core analyses such as paleontology， trace elements， clay minerals， carbon and oxygen isotopes， is applied in the study. The results show that the lithofacies assemblages of the E in the study area can be divided into 7 types， 5 of which are mixed lithofacies assemblages containing lime. Paleoclimate， paleo-provenance and deep-sourced fluids serve to jointly control the paleowater conditions of continental lacustrine basins， while the carbonate content is under the control of water salinity therein. The lime-rich areas are mainly located in the Tuo-Sheng fault zone， northern Caoqiao slope， central anticlinal and slope zones， while the lime-lean areas mainly in freshwater input regions and deep depression zones. Therefore， key turbidite exploration is supposed to be directed towards freshwater-affected areas adjacent to prodelta and freshwater-diluted areas in central depression.

10.11743/ogg20220205