Sequence stratigraphy and coal accumulation of shallow water delta systems under low accommodation conditions: a case study from the Lower Permian Shanxi Formation in Bohai Bay region
Chang Jia1, Chen Shi-Yue1, Wang Qiong2, Pu Xiu-Gang3, Yang Huai-Yu4
1 School of Geosciences,China University of Petroleum(East China),Shandong Qingdao 266580,China; 2 The Third Institute of Geology and Mineral Resources of Shandong Province,Shandong Yantai 264003,China; 3 PetroChina Dagang Oilfield Company,Tianjin 300280,China; 4 Research Institute of Petroleum Exploration and Development,Shengli Oilfield Company,SINOPEC,Shandong Dongying 257015,China
Abstract:The Lower Permian Shanxi Formation in the Bohai Bay region was studied to analyze the sequence stratigraphy and coal accumulation of shallow water delta systems under low accommodation conditions. According to the two types of subaerial unconformities(SU)including sedimentary facies transition surface and incised valley scour surface,the Shanxi Formation can be divided into three 3rd order sequences(Sq1,Sq2 and Sq3),each of which represents one stage of delta. Each 3rd order sequence is divided into LST,TST and HST system tracts by maximum flooding surface(MFS)and maximum regression surface(MRS),representing nine 4th order sequences. A series of sequence-specified sedimentary facies diagrams have been constructed based on the contours of lithological parameters. Under the controls of the accommodation space growth rate and peat accumulation rate,flood plain in delta plain and peat swamp in delta front are favorable coal accumulation centers,which are located in the eastern part of Jizhong depression,the middle northern part of Huanghua depression and part of Jiyang depression. Coal seams in the flood plain is thick,and the coal accumulation center tends to move southward with the advance of the shallow water delta. The coal accumulation environment in the delta front is relatively poor,and coal seams are relatively thin,which is easy to be washed by the underwater distributary channel sand bodies. The sequence stratigraphic and sedimentological analysis of the Lower Permian coal-bearing strata of the Bohai Bay region provides a basis for a comprehensive coal accumulation model establishment, which involves a five-period evolution from the LST,early TST,middle TST,late TST to HST. The major coal seams were accumulated in the TST and HST of the sequences Sq1 and Sq2. These results are of practical significance for coal resources exploration and enhance the geological effects of prospecting engineering in the Bohai Bay region.
Chang Jia,Chen Shi-Yue,Wang Qiong et al. Sequence stratigraphy and coal accumulation of shallow water delta systems under low accommodation conditions: a case study from the Lower Permian Shanxi Formation in Bohai Bay region[J]. JOPC, 2022, 24(2): 361-374.
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