Sequence Stratigraphy Of Carboniferous-permian In Bohai Bay Basin

With the continuous improvement of oil and gas exploration in the eastern part of China,there are fewer and fewer high-quality reserves in the middle and shallow parts of the Bohai Bay Basin,the deep strata have gradually become exploration hot spots.In order to insight into sequence stratigraphy of Carboniferous-Permian in Bohai Bay Basin,this paper use sequence stratigraphy theory as a guide,detailed survey of the typical Carboniferous-Permian field section in Taiyuan Jijiagou,Zibo Boshan,Xingtai Sabagou,Qinhuangdao Shimenzhai,Yuzhou Dafengkou,combined well logging data and earthquake data,ascertained classification scheme of sequence stratigraphic frame,analyzed field sections and well logging sequence stratigraphic features,illuminated sequence units plane distribution features,discussed coal-measure source rocks development characteristics and distribution rules under the sequence framework.The research results are as follows:There are 8 third-level sequence interface developed in the Carboniferous-Permian of the Bohai Bay Basin,including regional unconformity interfaces,transgressive direction conversion interface,incised valleys washing interfaces,local angle unconformity interfaces.Limestone,thick coal seam,sedimentary transformation surface and silicolites is represent maximum flooding surface.There are five kinds of subsequences,including tidal flat,platform,barrier island-lagoon,shallow water delta and fluvial.Tidal flat,platform and barrier island-lagoon subsequence are developed in the epicontinental sea sedimentary environment,shallow water delta,fluvial subsequence is developed in the transitional sedimentary environment,fluvial subsequence is developed in the continental sedimentary environment.According to the fluctuation of sea level and the descent of the base level,the Carboniferous-Permian in Bohai Bay Basin is subdivided into seven third-order sequence,fifteen fourth-order sequences.Sequence 1th to Sequence 3th is developed two-period transgression under the epicontinental sea sedimentary environment,which influenced by the change of global sea level.Sequence 4th is mainly develop in transitional sedimentary environment,which came up passive regressive because of source of supply increase.Sequence 5th to Sequence 6th is mainly developed in continental sedimentary environment,Yinshan-Yanshan orogenic belt became active in this time,and fluctuation of base level was the major control factors to sequence development.Sequence 7th is develop in fluvial and lacustrine sedimentary environment,which belong to a hot arid zone.Through comparison of sequence stratigraphic framework,Sequence 1th and Sequence 2th have the features of northeast thick and Southwest thin in Bohai Bay Basin,limestone of Sequence 3th become less and less vary from north to south in Bohai Bay Basin.Clastic grain sizes of Sequence 4th to Sequence 7th is coarsen obviously in the north of Bohai Bay Basin.Coal-measure source rocks types in the research area are coal seams,carbonaceous mudstones,dark mudstones.They are developed in the peat flat of lagoon-tidal facies and peat bog of deltaic plain subfacies.Through analysis and testing the samples of coal-measure source rocks,it can be knew that the abundance of organic matter in the source rocks of coal measures is generally low,with relatively dark mudstones being relatively good,the types of organic matter is dominated by type III kerogen and contains a small amount of type II2 kerogen.The maturation of organic matter is in the low-maturity stage.In vertical dimension,coal-measure source rocks are distributed in Taiyuan formation and Shanxi formation,part of them develop in Benxi formation.On the plane,coal-measure source rocks are distributed in Kongxi buried hill of Huanghua depression and Suqiao-Wenan area of Jizhong depression and western region of Linqing depression.