| Ordovician Marine Carbonate of Ordos basin in China is an important area of natural gas exploration and is also the main gas exploration targets of reserve and output increment in China.In this paper,taking Jingbian area of Ordos Basin as an example,researching the characteristics of natural gas migration,clearing the natural gas accumulation period,establishing the natural gas accumulation pattern and summarying the accumulation rule of gas accumulation by means of core observation,thin section identification,fluid inclusion determination,carbon isotope analysis of natural gas,basin evolution simulation and restoration of ancient landform.The study reveals that the sedimentary facies of Mawu1,Mawu2 and Mawu4 section of Ordovician in Erdos basin Jingbian area is mainly dolomite flat and calcite dolomite flat,belong to ultra low porosity and ultra low permeability tight reservoir,low sulphur dry gas reservoir,there is no edge and bottom water,mainly composed of lithologic and stratigraphic gas reservoirs and paleo geomorphic lithologic gas reservoirs.The natural gas in the Ordovician reservoir mainly came from Carboniferous-Permian coal source rocks,and some of them came from the source rocks of Ordovician carbonate rocks.With the effect of hydrocarbon generating pressurization in Carboniferous Permian source rocks,natural gas,in the late Jurassic and early Cretaceous,along the ancient trench,unconformity,migrated vertically and laterally into the slopes of weathering crust and ancient landform in high.Natural gas is mainly enriched in the five major elements of the coupling: the distribution area of the source rocks,dolomite flat and calcite dolomite flat area,the reservoir physical properties are better and the thickness of the larger area,the distribution of mudstone at the bottom of Benxi Formation,weathering crust and high and middle part of ancient landform. |
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