Hydrocarbon Accumulation Mechanism And Distribution In The Eastern Qikou Sag,Bohai Bay Basin

Bohai Bay Basin,located in the eastern part of China,is one of the most important oil and gas generating basins in China.Qikou Depression is located in the Bohai Sea.The eastern part of Qikou Depression is located in the mining area of China Offshore Petroleum.As one of the large sags in Boxi exploration area,the mechanism and distribution of hydrocarbon accumulation around Qikou Depression is naturally a hot topic in exploration and research of Boxi exploration area.The strata of Qikou Sag in Huanghua Depression are basement pre-Paleogene stratum,Paleogene fault depression stratum and Neogene depression stratum from bottom to top.The Paleogene Dongying Formation and Paleogene Shahejie Formation are important source rocks in Qikou Depression.The Neogene Minghuazhen Formation and Paleogene Shahejie Formation are the main oil-bearing strata in Qikou Sag.Qikou sag is a large high-quality hydrocarbon-generating sag.Three sets of main source rocks are developed from top to bottom,namely,the third member of Dongying Formation,the first member of Shahejie Formation and the third member of Shahejie Formation.The source rocks in Qikou Depression are large in scale and widely distributed,and the results of geochemical experiments of source rocks reveal that the Paleogene source rocks have entered the hydrocarbon generation threshold and are in the oil generation stage,indicating that Qikou Depression has a good oil source base.The following types of sedimentary facies are mainly developed in the eastern part of the Qikou sag: the delta facies(the braided river delta facies,the fan delta facies,the meandering delta facies),the alluvial fan facies,the nearshore subaqueous fan facies or the far shore facies fan facies.Lake phase(shore shallow lake phase,semi-deep lake phase,deep lake phase).In the period of the Shahejie period,the place where the relationship between the reservoirs and the reservoirs in the eastern part of the Qikou sag is better is located in the south of the Qikou sag.In the third period of the Shahe sag,the eastern part of the Qikou sag has the best relationship.The area includes the Qinan fault zone and the Shaxi skirt zone on the west side of the Shaleitian bulge.In the vicinity of the Qinan fault zone in the eastern part of the Qikou sag,the difference of oil and gas enrichment horizons has obvious regularity,which is believed to be caused by the difference in the activity of the main fault during the neotectonic movement.Based on this,it is concluded that the hydrocarbon accumulation model of the Qinan fault zone is as follows: 1.Main fault transport,secondary fault control.2.Sand body fault transport,main fault control.At the same time,according to the activity of the Shaxi fault in the eastern part of the Qikou Sag and the relationship between the storage and storage of the Shaxi skirt,the oil and gas accumulation model of the Shaxi skirt belt is summarized: the oil and gas is near-source accumulation.