咸化湖盆深部优质储集层形成机制与分布规律——以渤海湾盆地济阳坳陷渤南洼陷古近系沙河街组四段上亚段为例

Formation and distribution of the high quality reservoirs in a deep saline lacustrine basin: A case study from the upper part of the 4th member of Paleogene Shahejie Formation in Bonan sag, Jiyang depression, Bohai Bay Basin, East China

以渤海湾盆地济阳坳陷渤南洼陷古近系沙河街组四段上亚段为例,基于钻井取心,开展岩心常规分析、铸体和普通薄片鉴定、扫描电镜分析以及流体包裹体测试,依据所获数据资料系统研究咸化湖盆成岩环境演化及深部优质储集层发育主控因素。该咸化湖盆储集体经历了先碱后酸、碱酸交替的成岩环境,早期碱性成岩环境下大量碳酸盐胶结物充填原生孔隙,使储集体孔隙度由初始37.30%锐减到18.77%,也使原生孔隙免于压实,保留可溶蚀空间。中后期酸性成岩环境下,早期碳酸盐胶结物溶蚀增孔10.59%,深部优质储集层得以形成。膏盐岩、烃源岩、断裂体系及沉积体展布共同控制优质储集层分布,渤南洼陷沙河街组四段上亚段深部优质储集层位于北部陡坡带,埋深为3 400~4 400 m,岩性以近岸水下扇扇端细砂岩和部分扇中细砾岩为主。

The upper part of the 4 th member of Paleogene Shahejie Formation in Bonan sag, Bohai Bay Basin, East China was taken as the study object. Conventional core analysis, casting and conventional thin section inspection, scanning electron microscope observation, particle size analysis and fluid inclusion analysis were carried out on cores, and the data from these analyses and tests was used to find out the evolution of diagenetic environment of the saline lacustrine basin and the main factors controlling the deep formation of high quality reservoirs. The diagenetic environment of the saline lacustrine basin experienced alkali and acid alternation. In the early alkali diagenetic environment, large amounts of carbonate cement filled the primary pores, making the reservoir porosity reduce sharply from 37.3% to 18.77%, meanwhile, keeping the primary pores from compaction, and retaining the dissolution space. In the middle-late stage of acid diagenetic environment, early carbonate cement was dissolved, resulting in rise of reservoir porosity by 10.59%, and thus the formation of the deep high quality reservoirs. The distribution of high quality deep reservoirs is controlled by the development of gypsum salt rock, source rock, fracture system and sedimentary body distribution jointly. Deeply buried high quality reservoirs in the upper part of the 4 th member of the Shahejie Formation in Bonan sag are nearshore subaqueous fan-end sandstone and some fan-medium fine conglomerate buried at 3 400-4 400 m in the north steep slope.