TYPES AND DISTRIBUTION CHARACTERISTICS OF SHALLOW RESERVOIRS IN THE NORTH JIANGSU BASIN

There are three types of shallow reservoirs controlled by different key factors for hydrocarbon accumulation in the North Jiangsu Basin,respectively controlled by low maturity and high efficiency oil source rock in the lower-middle part of the Fu2 Member,fault of vertical migration pathway,and large scale sandstone for lateral migration.Distribution of shallow reservoirs is featured with hyperdispersion in the North Jiangsu Basin.Shallow reservoirs are developed in the Jinhu Sag and Gaoyou Sag in western basin,with various types and large scales.This distribution feature is correlated to the Tanlu Fault Belt controlling the structure and deposit evolution of basin as well as the key factors for hydrocarbon accumulation.The evidence is that the periphery of Tanlu fault depressions is well-developed of low maturity and high efficiency oil source rock in the lower-middle part of the Fu2 Member,sandstone in the bottom part of the Fu2 Member and the upper part of the Fu1 Member,forming abundant shallow reservoirs.Periphery Tanlu fault depressions are inherited from early deep rift with high geothermal gradient,with earlier matured oil.Faults are polyformative and of high density in the area near the Tanlu Fault Belt,which helps to form secondary shallow reservoirs of fault-passway type.Consequently,there are a lot of shallow reservoirs in the Jinhu Sag,the Gaoyou Sag and the Qintong Sag around the Tanlu Fault Belt.Shallow reservoirs distributed over the growth fault zone and the strike-slip flower fault system in inner-outer slope.There is a great exploration potential in the North Jiangsu Basin,if we aim at the three types of shallow reservoirs,and focus on their forming and distribution rules in these areas.