Shale Gas Exploration Potential And Resource Evaluation In The Western Margin Of Ordos Basin

In this paper,the western margin of Ordos Basin is taken as the main study area,and shale section rich in organic matter in Carboniferous Permian and Triassic is taken as the target section.Based on the full investigation of literature at domestic and international,investigating and analyzing the related research results and data,through methods such as geological field exploration,sample collection and laboratory analysis,investigating and doing research on enrichment strata and distribution range,geochemical characteristics such as organic matter content,kerogen type,organic matter thermal maturity,hydrocarbon generation ability,and reservoir characteristics such as mineral components,porosity and pore structure,as well as the characteristics of gas content of the shale rich in organic matter.Tracking the dynamic frontier scientific and technological achievements at domestic and international on shale gas formation mechanism,accumulation conditions and enrichment rule,analyze the shale gas resources potential,predict favorable area and calculate potential the amount of shale gas resources in the western margin of Ordos Basin,in order to make some contributions to shale gas exploration work in Ningxia area.Based on the research results,Shanxi formation,Taiyuan formation and Yanghugou formation in Carboniferous-Permian of Upper Paleozoic in the western margin of Ordos Basin have small sedimentary shale thickness,the average thickness of shale rich in organic matter is less than 30m,and the thickness is more than 30m in some area,the buried depth of shale of the three formation is mainly 500m~4500m in the most area in the study area.The mean value of total organic carbon content is above1.0%,organic matter is mainly type II,vitrinite reflectance,the mean value of Ro in more than 1.2%,the mineral component is mainly composed of clay minerals,developing a number of micro pores and micro fractures.The mean values of gas content in Shanxi formation,Taiyuan formation and Yanghugou formation are 0.58m~3/t,0.79m~3/t and 1.51m~3/t,both of which are above 0.5m~3/t.Sedimentary shale thickness of Yanchang group in the west margin of Ordos Basin is very large,the average total thickness of shale is more than 300m,and the average thickness of organic shale is close to 40m,the buried depth is 10.5m~2559m.The total organic carbon content is above 2.0%,organic matter is mainly type II,the mean value of Ro is around 1.0%,the minerals are mainly composed of brittle minerals such as quartz and feldspar.developing some micro pores and micro fractures.The average value of shale gas content is 2.21m~3/t.Through the summary and study of geological features of shale of the that in the western margin of Ordos Basin,Carboniferous-Permian Shanxi Formation,Taiyuan formation,Yanghugon formation as well as the Triassic Yanchang group have the conditions for shale gas generation and accumulation.Referencing domestic and international shale gas evaluation standard,combined with the actual geological conditions in the study area,working out the selection standard for shale gas favorable areas in the study area,and using the risk factors superposition method,selecting two favorable area in Shanxi Formation,one favorable area in Taiyuan Formation,one favorable area in Yanghugou formation,and one favorable area in Yanchang group in the western margin of the Ordos Basin.The shale gas resources amount of the four favorable areas is about 8419.53 billion cubic metres.A large amount of shale gas resources indicates that the western margin of Ordos basin has certain potential for shale gas exploration.