SEQUENCE ARCHITECTURES AND SEDIMENTARY FEATURES OF LOWER CRETACEOUS IN THE SOUTHERN SONGLIAO BASIN

Based on an integrated analysis of geologic,seismic and drilling data,the Lower Cretaceous Shahezi Formation-Quantou Formation(K1sh-K1q1)in the southern Songliao Basin are divided into 5 second-order and 14 third-order sequences,which consist of the sequence stratigraphic framework in southern Songliao basin.The 5 second-order sequences are grouped into 3 types,including rift,rift-depression transient,and depression.Tectonic movements determine the types of sedimentary faces in the study area,the distribution of which appears as combinations of volcanics-alluvial fan-braided river-braided river delta-lake-underwater gravitational flow,alluvial fan-fan delta-lake-underwater gravitational flow,and meandering river-braided river.The clastic reservoirs in the study area are dominated by fan delta system in Shahezi Formation,alluvial fan system in the Yingcheng Formation,braided river system in Denglouku Formation,and meandering river system in the first member of Quanzhou Formation.The reservoir lithologies are dominated by medium-and coarse-grained conglomeratic sandstone and medium-and fine-grained sandstones,followed by siltstone,with oil and gas shows mostly occurring in fine sandstone.