The Sequence Stratigraphic Division And Sedimentary Facies Study Of Guantao Formation In Huanghekou Sag

Huanghekou Sag is located in the southeast of Bohai Bay Basin,with a higher degree of exploration.Guantao formation of the sag is the important stratum of oil reservoirs exploration.Therefore,making a study of the sequence stratigraphy of Guantao formation is the base of finding the non-structural reservoirs in the stratum,which will make an important practical significance.Even though the Guantao formation of Huanghekou Sag is a continental stratum,it deposited in the shallow water environment of lacustrine basin shrinking period and its lake level changed frequently and its sequences developed atypically,so that the recognition of the stratum is difficult now.The theory and technique of shrinking shallow water lacustrine basins isn't perfected,so the researchers may establish different sequence statigraphy frameworks in the same area.Therefore,making a study of sequence stratigraphy of Guantao formation is the complement of the study of the theory and technique of continental sequence stratigraphy,which makes a theoretical significance.Based on the innovation-type technique of circle analysis,boundary recognition,well-seism restrict,closed net and refine,the Guantao formation can be identified 3 sequence boundaries which includes: SB2?SB21?SB0,and 2 maximum flooding surfaces which includes: mfs L?mfs U,so that we divide 4 system tracts which includes: ESTg L?HSTg L?ESTg U?HSTg U,and 2 third-order sequences which includes: SQg L and SQg U,with which the exact isochronous stratigraphic framework can be established by.With the restrict of the exact isochronous stratigraphic framework,the analysis of sedimentation can be carried out by setting system tracts as lengthways elementary units.On the base of petrologic features,logging features and seism features,the Guantao formation can be identified 3 sedimentary facies: braided river facies,braided river delta facies and lacustrine facies,including 5 sedimentary subfacies and 10 sedimentary microfacies.With the horizontal distribution characteristics of san factor and heavy mineral,the provenance of north-west,south-west,south-east and north-east can be identified.But in each system tract,the provenance of every direction has a little difference.Based on sedimentary facies and provenance systems,the horizontal distribution characteristics of sedimentary subfacies can be identified by single well-well tie sedimentary facies and seismic facies.We can analyze that during Guantao formation,braided river facies,braided river delta facies and lacustrine facies developed from the out of sag to the inside sag,and the range of the lake become bigger and the provenance become poorer.Because of large area of braided river facies,the sand factor is higher,which has an important significance for oil-gas exploration.