Tectonic evolution and hydrocarbon accumulation of Laizhouwan depression in southern Bohai Sea

Laizhouwan depression in the southern Bohai Bay is complicated in hydrocarbon accumulation and is low in exploration maturity.An oil discovery with reserves around hundred millions of tons was obtained recently.Laizhouwan depression is characterized by fault depression and strike-slip inversion.According to the feature and strength of fault activity,the faults were divided into three types which have different control on depression pattern,sedimentary system and hydrocarbon migration system.Furthermore,the tectonic evolution of Laizhouwan depression was divided into three stages: the early rifting stage during deposition of the Kongdian Formation to the Member Ⅲ of Shahejie Formation,the strike-slip stage during deposition of the Member Ⅱ of Shahejie Formation to Dongying Formation and the late activation stage since the Neogene.The tectonic evolution controls trap formation,sediment filling,subsidence center migration,and source rock formation and evolution.The late strong tectonic and volcanic activities are helpful for late hydrocarbon accumulation in Laizhouwan depression.