Sedimentary Facies And Reservoir Charaeteristics Of The Lower Cretaceous In Northern Area Of Saihantala Sag

Guided by the theories of sequence stratigraphy and sedimentology , the sequence stratigraphy,sedimentary facies and reservoir characteristics of lower Cretaceous in the northern Saihantala sag have been studied in detail based on the geological, well logging, seismic and testing data.Through the combination of seismic and logging data, the formation from Aershan set to Tengger set in the study area can be divided into 3 third-order sequences(S1,S2,S3) and 6 fourth-order sequences (S1-1,S1-2,S2-1,S2-2,S3-1,S3-2). On this basis, sequence stratigraphic framework is established after the medium-term and short-term base level cycles are identified.The types and the characteristics of sedimentary facies have been concluded which includes the alluvial fan,subaqueous fan facies, the braided river delta facies, the lacustrine facies and the turbidite fan facies, etc.The plane distribution characteristics of sedimentary facies are as follows: the alluvial fan and braided river delta facies were deposited in the northern area; rivers-braided delta facies and shallow lake facies were distributed on Chagan slope in the western area; Subaqueous fans were developed under the uplift in the southeastern, while turbidite fan facies and deep lake facies were developed in the deep water area of the basin.Reservoir properties and pore structures change greatly in the study area depending on the sedimentary facies types, the lithology characteristics, the buried depth and the diagenesis. three categories(Classâ… , Classâ…¡, Classâ…¢) of reservoir have been classified: high porosity and permeability(Classâ… reservoir); medium porosity and permeability(Classâ…¡reservoir ); low medium porosity and permeability(Classâ…¢reservoir).