Sequence Stratigraphy And Depositional Systems Of Shahezi Formation In Fulongquan Fault Depression,Songliao Basin

Fulongquan fault depression is located in the south of Songliao basin,which is a graben basin during the early Cretaceous.In Fulongquan fault depression,there are Gujiadian sub-sag,Funan sub-sag and Fubei sub-sag from the south to north.Based on sequence stratigraphy,structural geology,sedimentology,this paper has established sequence stratigraphical framework and analyzed sedimentary systems systematically,and then predicted the favorable reservoir distribution.According to the data of cores,frilling,logging and 3D seismic,in Fulongquan fault depression,Shahezi formation can be divided into three third-order sequences(SQ1,SQ2 and SQ3)and each sequence is further devided into LST,TST and HST.The characteristics of them are different with the migration of sedimentary centre and subsidence centre.During the early stage of the Shahezi formation,the sedimentary centre was in the Gujiadian sub-sag,and then the sedimentary centre migrated to the north gradually.In the late stage of Shahezi formation,the sedimentary centre was in the Fubei sub-sag.In the East of Fulongquan fault depression,three main boundary faults,from south to north,controlled the development of Gujiadian sub-sag,Funan sub-sag and Fubei sub-sag.Through analyzing heavy minerals,sandstone percentage,paler-geomorphology characteristic,as well as a few seismic attributes,there are two major provenance systems.The northwest of Fubei sub-sag and the southwest of Gujiadian sub-sag are the main provenance areas.In combination with core facies,logging facies and seimic facies,there are fan delta facies,nearshore subaqueous fans facies and lake facies.Fan delta plain and fan delta front are the two main sub-facies in fan delta system.Fan delta front is the main part in this area,and underwater distributary channel,distributary bay are the most common micro-facies.In addition,nearshore subaqueous fans facies can be found in the east of Funan sub-sag.In Shahezi formation,incised-valley traps,lenticular sand traps,sandstone updip pinch out traps and structure-lithology composite traps are the typical types of the traps.In combination with the quality and distribution of hydrocarbon source rocks,as well as reservoir types and distribution,four favorable exploration zones are predictedin Shahezi formation.