从青海湖现代沉积看鄂尔多斯盆地延长组滩坝砂体的发育与保存

Study on the development and preservation of shore-shallow lacustrine beach and bar of Yanchang Formation in Ordos Basin based on the modern sedimentary characteristics of Qinghai Lake

基于对青海湖滩坝砂体形成和保存条件研究的认识,应用"将今论古"的研究方法,从物源供给、湖盆底形、风动力-水动力、湖岸线形态及湖平面变化(层序演化)等方面,对现代青海湖与鄂尔多斯盆地滨浅湖滩坝沉积进行了对比研究。认为鄂尔多斯湖盆在上三叠统延长组沉积期间,长9—长82—长7沉积期既处于二级层序的早期,同时又位于三级层序湖侵体系域,十分有利于陆源碎屑滩坝的保存。建立了延长组滨浅湖滩坝砂体分布的预测模型,指出盆地南部(包括西南部与东南部)是长9—长82—长7期滩坝砂体发育与保存的有利地区,也是未来寻找滩坝型油气藏的有利地区。

Based on the understanding for the formation and preservation conditions of the beach and bar sand bodies in Qinghai Lake, using the basic principle of "the present is the key to the past" in geology, this paper carried out a comparative study on shore-shallow lacustrine beach and bar deposits in modern Qinghai Lake and ancient Ordos Basin from the the aspects of provenance supply, topography of lake basin,(wind) hydrodynamic force, lake shoreline morphology and lake level cycle(base level). It is considered that during the deposition of Yanchang Formation in Upper Triassic, Chang9-Chang82-Chang7 sedimentary period is not only in the early stage of second-order sequence, but also in the lake transgressive system tract of third-order sequence, which is very conducive to the preservation of terrigenous clastic beach and bar. The prediction model of the distribution of shore-shallow lacustrine beach and bar of Yanchang Formation is established. It is pointed out that the southern basin(including southwest and southeast) is a favorable area for the development and preservation of the beach and bar sand bodies of Chang9-Chang8_(2)-Chang7, and is also a favorable area for looking for the favorable beach and bar reservoirs in the future.