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鄂尔多斯盆地长期存在“南油北气”的固有认识,晚古生代早期砂体不发育与分布规律不清的认识,长期制约了盆地东南部天然气勘探开发的步伐。因此,加强盆地东南部上古生界煤系含气地层地质方面的研究、尤其是层序地层与储集砂体成因研究,对进一步增储上产具有重要理论与实践意义。作者采用Vail经典层序地层理论与方法,对鄂尔多斯盆地东南部上古生界进行层序地层研究:首先对层序界面进行识别,以岩性、旋回和沉积特征变化作为识别依据,并提出二级层序界面上下岩性组合变化巨大、二级界面之上叠置的低位砂厚度巨大的观点,共将本溪组—石盒子组划分为3个二级层序,11个三级层序;其次根据层序内部砂体堆积、迁移样式对体系域进行了划分。通过大量钻井的层序单元追踪对比与岩心精细描述,重点分析层序格架内主要含气层段本溪组、山西组及盒8段储集砂体的空间叠置关系,结合不同时期基准面旋回变化及其形成机制对其进行探讨,认为优势含气层段储集层中本2段具有障壁迁移、毯式连通,山2段具有低位控砂、面线连通,山1段具有侧向迁移、接触式连通,盒8段具有迁摆叠置、多向连通的特点。
Ordos Basin long-standing “Nankou North Gas” inherent understanding of the late Paleozoic sand bodies are not well-developed and unclear distribution of understanding of the law, long restricted the southeastern gas exploration and development pace. Therefore, it is of great theoretical and practical significance to enhance the geology of the Upper Paleozoic coal-bearing gas-bearing strata in southeastern part of the basin, especially the study on the genesis of sequence stratigraphy and reservoir sand body. Using the Vail classical sequence stratigraphy theory and method, the authors studied the sequence stratigraphy of the Upper Paleozoic in southeastern Ordos Basin. Firstly, the sequence boundary was identified, and lithology, cycle and sedimentary characteristics were taken as the identification basis, The Benxi Formation-Shihezi Formation is divided into three second-level sequences and eleven third-level sequences in the view of huge changes of the upper and lower lithologic assemblages in the sequence boundaries and huge low sand thickness superimposed on the secondary interfaces. According to the sequence of sand body accumulation and migration pattern, the system domain is divided. Tracing the contrast and core fine description by a large number of drilling sequence units, focusing on the spatial superposition relationship of the Benxi Formation, Shanxi Formation and the 8th member reservoir sandstone in the main gas bearing intervals in the sequence framework, Cyclone variation and its formation mechanism are discussed in this paper. It is concluded that the first two stages of reservoirs in the favorable gas-bearing intervals have barrier migration and carpet connectivity, Migration, contact-type connectivity, Box 8 with the migration stack, multi-directional connectivity.