Distribution Characteristics Of Biodegradable Gas Of Gaoyou Sag,Northern Jiangsu Basin

The natural gas resources in the North Jiangsu Basin are mainly distributed in Gaoyou Sag(125-24.9 billion square meters)and Jinhu Depression(38-76 billion square meters),accounting for 70%and 22%of the total natural gas resources respectively.The natural gas resources in Gaoyou Sag are extremely abundant.The basin is rich in oil and poor in gas,but some shallow biodegradable gas reservoirs have been found in the process of oil exploration.The predecessors mainly focused on the Paleozoic new thermal storage gas in Yancheng sag,and did not carry out systematic research and targeted exploration for biodegradable gas and new thermal storage gas,and the distribution characteristics of degraded heavy oil were unclear.Because biodegradable gas has the advantages of shallow burial and easy exploitation,it is urgent to study biodegradable gas reservoirs in Gaoyou Sag,Northern Jiangsu Basin.The North Jiangsu Basin in the study area is located in the continental part of the North Jiangsu-South Yellow Sea Basin.Its north and South are bounded by the South Jiangsu uplift and the ancient land of Lusu,respectively.The West is to the Tanlu fault,and the East is to the South Yellow Sea Basin.The basin area is about 3.8 x 104 km~2.After investigation,Gaoyou Sag has good gas source conditions and abundant gas resources.According to the classification criteria of heavy oil reservoirs in China petroleum industry,heavy oil in Northern Jiangsu Basin is divided into primary low-immature heavy oil(Class I)and secondary biodegradable heavy oil(Class II),in which biodegradable gas is mostly generated by secondary heavy oil.On the basis of defining the basic characteristics and genetic mechanism of heavy oil reservoirs in the area,the heavy oil zone in Gaoyou Sag of Northern Jiangsu Basin is basically determined,which mainly distributes in Zhouzhuang,Xuzhuang and Huangjuan of the southern fault terrace zone and Weizhuang of the western part of the northern slope.The distribution area of Gaoyou biodegradable gas reservoir is preliminarily predicted.Based on the background of Gaoyou Sag in Northern Jiangsu Basin,and guided by the theoretical knowledge of petroleum geology,Microbiology and geochemistry,this paper comprehensively compares and analyses the reserves reports and a large number of oil and gas testing data of each oilfield in this area,as well as the chromatographic maps of crude oil in heavy oil area,and carries out the main geological environment preservation conditions of fault blocks Wei 8,Huang 5 and Xushan1 in the predicted area.The horizontal distribution area of biodegradable gas reservoirs in Gaoyou Sag is confirmed by analysis and verification,and the vertical stratigraphic characteristics are studied and analyzed.It is confirmed that biodegradable gas reservoirs in Gaoyou Sag are mainly distributed in Weizhuang,Xuzhuang,Zhouzhuang and Huangjuan in plane,and in Funing Formation,Dainan Formation and Sanduo Formation in vertical direction.It is clear that shallow heavy oil is biodegradable,and the degradability of crude oil in Wei5,6,8,Xuzhuang,Zhouzhuang,Shawei,Euro-North and Dongyang fault blocks is slight to moderate.Heavy oil is formed in the high distal part of oil and gas migration in fault terrace zone and slope area.The feasibility of searching for biodegradable gas reservoirs based on heavy oil distribution zones and exploration models based on biodegradable gas reservoirs is verified theoretically,which provides theoretical guidance for the reservoir formation model and exploration practice of biodegradable gas reservoirs in North Jiangsu Basin.