Hydrocarbon Accumulation Mechanism Of Typical Buried-hill Belts In Jizhong Depression,Bohai Bay Basin,China

Deep buried-hill belts have become the important target area in the Jizhong Depression,Bohai Bay Basin.With the increasing exploration degree,the theoretical research of hydrocarbon accumulation mechanism is urgently needed to guide the next stage of oil and gas exploration.The Hexiwu and Shulu buried-hill belts in Jizhong Depression,Bohai Bay Basin are selected as the object because they are typically inherited and anti-transformation slopes,respectively.The main objective of this study is to investigate the complex hydrocarbon accumulation mechanism and processes of the typical buried-hill belts through a combination of geological,geophysical,and geochemical analyses.The main purposes of this dissertation include:(1)to reconstruct the thermal history and illuminate the hydrocarbon kitchen evolutionary feature,(2)to examine the genetic type and source of the hydrocarbon,(3)to illustrate the main controlling factors and mechanism of hydrocarbon accumulation,and(4)to reconstruct hydrocarbon accumulation models.The results show that Jizhong Depression has experienced two heat flow peaks during the late Early Cretaceous and the Eocene,with heat flow values of 78 mW/m2?82 mW/m2 and 80 mW/m2?85 mW/m2,respectively.The secondary hydrocarbon generation threshold of the Carboniferous-Permian coal-bearing source rocks in the northern Jizhong Depression is about 3550 m,and the hydrocarbon kitchen is mainly located in the east of Langgu sag,Damengzhuang subsag and the northeastern area of Wen'an slope,and the contribution rate of Carboniferous-Permian is mainly 50%?80%.The oils in the northern Hexiwu buried-hill belt are mainly derived from the mixed source of the fourth member of Shahejie and Kongdian formations and Carboniferous-Permian source rocks,whereas oils in the southern Hexiwu buried-hill belt are mainly derived from the fourth member of Shahejie and Kongdian formations,and the oils in the Shulu buried-hill belt are mainly derived from the third member of Shahejie formation source rocks.Two hydrocarbon accumulation models of the Hexiwu buried-hill belt are established.The hydrocarbon accumulation models in the northern part of the Hexiwu buried-hill belt can be summarized as the double-depressions providing hydrocarbon-fault and unconformity transport-multilayer accumulation system,while the models in the south of the belt can be concluded as single depression providing hydrocarbon-fault transport-top layer accumulation system.The distribution and accumulation of hydrocarbon were probably controlled by source rocks,reservoir heterogeneity and migration system.In addition,two hydrocarbon accumulation models of the Shulu buried-hill belt have been summarized as unconformable transport-reverse fault block accumulation system and fault transport-faulted anticline accumulation system.The source rocks,shielding of reversed faults and preservation conditions all have significant impacts on the variations in hydrocarbon distribution and accumulation.The results of this thesis not only enrich the theory of petroleum geology in the buried-hill belts,but also provide theoretical and scientific basis for oil and gas exploration for buried-hill belts in the Jizhong Depression.