Study On Depositional Systems And Lithofacies Paleogeography Of He-8 Period, Erdos Prototype Basin

Erdos basin is rich in resources including oil,coal,natural gas, etc. And there is broad areas for exploration, multi-gas series of strata, and a large area of multicycle craton super imposed basin. As an important gas bearing layer, the research about the He 8 of reservoir of lower Shihezi formation is of great significance.On the basis of predecessor’s achievements, the paper is guided by the theory of modern sedimentary geology, sequence stratigraphy and petroleum geology theories as a guide, started from the perspective of prototype basin, carried out the research on boundary type, source direction of prototype basin, depositional system and lithofacies paleogeography in North China Basin, where the Ordos Basin locates. The research referred to the geological background of tectonic and sedimentary in North China Basin of He 8 as a basis, and was based on the measured data field section, core data, combined with logs and geochemical data, particle size analysis data, general information sheets, etc, obtained several achievements as follow.The paper has made clear the four types of boundaries in North China Basin. The northern boundary of the basin mainly located in Xing’an Mongolian orogenic belt is a sedimentary boundary. The southern boundary located in the Qinling-Qilian tectonically active zone is a denudation boundary. The eastern boundary Located in the Dan Lu fault zone is a fault boundary. The western boundary is the thrust napped belt of a series of thrust fault structure, where the original boundary has been completely transformed, thus it is a transformed boundary.Through outcrop survey, sampling and laboratory analysis and testing of samples tested,combing the characteristics of the ancient basin, utilizing light and heavy mineral assemblages, palaeocurrents,REE distribution characteristics and gravel and many other indicators, we draw a conclusion that the northern source is the main source direction, northwest is also one of the provenance directions, while southwest and southern provenance influences relatively little.Using outcrop and well data of North China Basin, combining to the regional deposition pattern and deposition characteristics, it can been found seven depositional system of alluvial fan, rivers, delta, lakes,flood plain and marine facies from lower Shihezi formation to He 8 formation.Sedimentary facies of the He 8 period in large North China basin in the plane has the following characteristics: subdivision of belts in north-south direction and differentiation of areas in east-west direction. From the north to the south distributed the alluvial fan-rivers- fluvial flood plain-Delta- tidal flat and lagoon. The west facies belts are not completely developed, but the eastern one is complete. Northern facies: it is alluvial fan in the west,and it is river in the east, central facies: the western area is fluvial flood plain, the eastern area is delta,southern facies: the western area is lake flooding, an the eastern area is shallow lake,the southeast is tidal flat.During He 8 period, from the edge of the Ordos prototype Basin to the basin center presents the following characteristics: alluvial sand, rivers facies sand, floodplain sand and other types of sand reservoir develope in order, The reservoir sand bodies are thick and widely distributed, which show belt-large area of blanket distribution characteristics from north to south direction.