The Study On Sedimentary Characteristics And Accumulation Control Factors Of The Lower And Middle Jurassic Yan'an Formation 9 In Zhenyuan-Jingchuan Area, Southwest Of Ordos Basin

Ordos basin is a multi-cycle superimposed basins, being the second largest of China's land sedimentary basin, internal tectonic activity minimal, containing oil, gas, coal, salt and metal Ur ores, and other resources, and has now become an important energy base of China.With the deepening of the process of exploration and development in this basin in recent years, and a large amount of geological information, logging information and production data have been accumulated. Based on above research, the geological evolution and the sedimentary features of Ordos basin have been knowed clearly, but the detailed research with production practice on local small-scale geological block is still in the initial stage, which was mainly due to the weak of geological information and its own limitations in the development stage of Geology. So the detailed research on local geological features and sedimentary characteristics of Ordos basin have their inevitability and necessity as the whole basin supplementary geological information and corroboration.The Zhenyuan-Jingchuan area located in the southwest of the Ordos Basin, previous oil studies mainly focused on YanChang formation in Triassic, and the studies on geological features and sedimentary characteristics of Yan'an Formation in Jurassic are very rare. In view of this, the author integrated and analysed the historical research results and the latest profile in the field section, outcrop, core observation and logging, seismic and other geological data of Zhenyuan-Jingchuan area in Ordos basin, using the methods of High-Resolution Sequence Stratigraphy, Sedimentology, Petroleum Geology, and other related disciplines, the systemic analysis and study about sedimentary characteristics and reservoir forming dominated factors in Yan9 member of Yan'an Formation in Jurassic were carried out.The Yan9 member can be further subdivided into Yan9~1 ,Yan9~2 ,Yan9~3 by those technologies such as elevation comparison,cycle controling, microtome method, and then compared the structural feature of these three sub-layers, the author think that the structural was charactered by nose-shape uplift which located on a gently monocline structure inclining to the west from east, and the sedimentary facies of Yan9 member belongs to river-deltas, and sedimentary subfacies belongs to deltaic plain, its provenance mainly come from the southwest of the basin. Through observation to the cores collected from more than 20 coring wells, four forms sedimentary subfacies that are distributary channel, crevasse splay, floodland, levee are identified. Integrated regional geological features, sedimentary characteristics, fine structure, reservoir characteristics, and many other factors, The main control factors for formation onYan9 reservoirs can be listed as follows: (1)Early Jurassic palaeogeomorphology; (2)differential compaction; (3) sedimentary subfacies; (4)up-diped lithologic tightbarrier.