Research On The Sedimentary Facies And Lithofacies Palaeogeography Of Ma5～5 Up To M6 Section In Area Of Nanniwan-Linzhen, Ordos Basin

The Paleozoic erathem of Ordos basin was possessed abounded gas resources. Especially, many high production gas wells were founded in Majiagou formation of low Ordovician recent years, which was the target sequence of next exploration. Under the guidance of stratigraphy, petrology, sedimentology and well logging interpretation, using a mass of field investigation data, well logging data, core description, statistical data and experimental analysis, this paper mostly researched the stratigraphic classification and sedimentary facies of Ma5-5 up to M6 in Nanniwan-Linzhen area.Concerning the division and correlation of stratum, this article ensured eight standard layers of especial lithological and electrical characters referred to the regional standard layers and logging curves'features. The stratum was subdivided to M6, Ma5-5-Ma5-1submember and correlated with the well of adjacent region.With regards to the sedimentary facies, a great amount of work was done. Firstly, based on the core description, logging data, experimental data and identification of fossils, the sedimentary characteristics was described in detail. Secondly, this research considered that the region was belonged to platform sedimentary system, and identified 3 subfacies and 8 microfacies, including gypsolyte and gypsolyte-bearing gypsum-dolomite, etc. Thirdly, using single factor analysis and multifactor comprehensive mapping method, the paper selected the content of dolostone, limestone, gypsum and strata thickness as the single factor to analysis the sedimentary facies feature of small strata separately. Then the evolution characters of paleogeography were studied, illustrating that the area had gone through a sedimentary cycle, which was open-platform in Ma5-5, restricted platform in Ma5-4 to Ma5-1, and open-platform again in Ma6. Furthermore, the terrain feature of the area had been analyzed. The northern of area was higher than the southern, which was bordered by the line of Y110-Y175-Y128.Come to a conclusion, these results filled a gap of the strata and microfacies in Nanniwan-Linzhen area, which has an important meaning to next exploration.