SEQUENCE-STRATIGRAPHY AND THE BASAL BOUNDARY OF THE GUANTAO FORMATION IN THE MIDDLE BOHAI GULF BASIN
ZHANG Ruo-xiang 1),LI Jian-ping 1),LIU Shi-lei 1),LU Hui-nan 2),ZHU Wen-sen 1)and WANG Bao-quan 1)1)Technical Department of CNOOC Ltd,Tianjin 300452;2)Nanjing Institute of Geology and Palaeontology,Chinese Academy of Sciences,Nanjing 210008
The sequence stratigraphy of the Guantao Formation was investigated by integrating lithostratigraphic,well log,paleontological,and seismic stratigraphic data.Three system tracts,LST(low-stand system tract),TST(transgressive system tract)and HST(high-stand system tract)were recognized.Base on base-level cycle analysis,three kind of base-level cycles(SSC:short-term baselevel cycle sequence;MSC:medium-term baselevel cycle sequence;and LSC:long-term baselevel cycle sequence)in Guantao Formation were recognized.The Guantao Formation is divided into two LSCs and four MSCs(MSC1 to MSC4).The depth of 2782 to 2917 meter of the D5-1 well belongs to the Dongying Formation,whose upper boundary marks the base of the Guantao Formation.Ascertaining the lower boundary of the Guantao Formation and a detailed sequence stratigraphic investigation of the Dongying Formation provide important stratigraphic basis to support the oil and gas exploration in the middle Bohai Bay Basin.
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