Physical Properties Evolution and Hydrocarbon Accumulation of Paleogene Nearshore Subaqueous Fan in the Eastern North Margin of the Dongying Depression

Taking the nearshore subaqueous fan of the third member and the forth member of the Shahejie Formation in the eastern north steep slope zone in the Dongying depression for an example,this study using multiple methods obtained the quantitative functional relationship between the physical properties cutoff values of the effective reservoir and the buried depth,on which the evolution of porosity with depth increasing in different subfacies of nearshore subqueous fan and its controlling on hydrocarbon accumulation were discussed. For the nearshore subqueous fans buried less than 3200 m,their inner fan,middle-fan and fan can develop effective reservoirs,forming such reservoir types as self-generating and self-reserving or generating in older but reserving in younger formation structural reservoir and the structural-lithologic reservoirs. For the nearshore subqueous fans buried over 3200 m,the physical properties of the inner fan are lower than the cutoff,so there were no effective reservoirs developed; the sand-conglomerate of the middle-fan developed more effective reservoirs. The change of the physical properties resulted in the of self-generating and self-reserving reservoirs which depend on lateral of inner fan and covering of lacustrine mudstone,and are characterized by outer fan migration,middle-fan accumulation,inner fan sealing ,and the middle-fan formed the self-generating and self-reserving lithologic reservoirs.