Study Of Sedimentary Characteristics Of Middle-late Proterozoic In West Margin Of Ordos Block

Not only the research of middle-lade sedimentary Proterozoic feature and evolution of Western trough of Ordos basin ware guiding significance to crust evolution of Proterozoic, but also it is very important to oil exploration to middle-late Proterozoic. The thesis is based on field section, logging, seismic, drilling, core and kinds of analysis test datas, with guidance of basin dynamics and sedimentology, combined with paleontological fossils, is topic geochronology, formation comparison symbol and sedimentary feature, the analysis of formation sedimentary is got. The basis of geochemistry of rock, with tectonic setting and lithofacies, the following results are got with evaluation of hydrocarbon genesis conditions of the middle-late Proterozoic.According to the regional stratigraphic correlation and sedimentary characteristics, combining ancient fossils, isotopic chronology analysis, and so on, the middle-late Proterozoic is divided into the Changcheng System, the Jixian Syetem and the Sinian System(the Qingbaikou System is lack).And the regional stratigraphic framework is established. There is a sedimentary cover which is most of Binhai- Neritic facies terrigenous sand, shale and carbonate rocks and is few volcanoes. The Changcheng system is mainly a set of terrestrial facies-littoral facies of quartz sandstone sedimentary, the source of the Changcheng system mainly comes from the craton. The Jixian system are mainly carbonate tidal flat sedimentary environment. The sinian system is a set of Marine drift conglo-Merate.The scope and the sedimentary thickness decreases from the Changcheng system -the sinian system in Ordos region. The Ordos region of the neoproterozoic is the tectonic setting of continental margin depression in qilian trough, and is a state of tension, The Helan chasmic trough is a graben subsidence zone which is deep within the north China landmass. The main hydrocarbon source rocks of the middle-late Proterozoic may be development horizon of the Jixian system in Ordos region of the Qilian trough, the organic carbon content of dolomite of the Jixian system is overall low, and is poor hydrocarbon source rocks. The organic matter type is I type, the maturity is mainly between 1.51%-4.68%, it is high maturity,and mainly is in the anger stage. The black shale witch is high organic matter abundance and high thermal evolution is found in the formation of the Changcheng System, and is good hydrocarbon source rocks. According to the prototype basin of the middle-late Proterozoic of the ordos region qilian trough and the hydrocarbon source analysis results, the oil and gas exploration direction of the middle-late Proterozoic mainly has two aspects:(1) The self-generated gas reservoir; (2) The gas reservoir which is below to the formation produced gas. The gas reservoir which is below to the formation produced gas is in the basin ’northern uplift area. We predict that the self-generated gas reservoir the middle-late Proterozoic is located in the basin rift trough of the southwest margin of basin.