Fan delta sedimentary system and facies models of Dainan Formation of Paleogene in Gaoyou Sag

Fan delta,which is developed on the steep slope belt on the south side of the sag,is an important sedimentary facies of Dainan Formation in Gaoyou Sag of Subei Basin.It is a very important oil exploration area in Gaoyou Sag.According to the data of core,well-log,seismic,granularity analysis and other information,a comprehensive study on fan delta sedimentary characteristics of Dainan Formation of Paleogene in Gaoyou Sag were conducted,and the sedimentary facies models of Dainan Formation were established.According to single well and cross well sedimentary facies analysis,seismic profile reflection and sand ratio contour map analysis,planar distributions of sedimentary facies in different submembers of Dainan Formation were confirmed,and the distribution maps of sedimentary facies in different submembers were drawn.The results showed that the steep slope paleogeography in the southern part of Gaoyou Sag was a suitable condition for the development of fan delta,and the lithologic characters reflecting shallow water environment were discovered,and the low component and textural maturities reflected the conditions of near provenance of sediments,and sedimentary structures reflecting traction flow and gravity flow were found;based on the seismic reflection profile,the reflection configuration was unstable,wedge shaped seismic facies toward the edge of the basin was developed.Finally,fan delta was divided into three parfacies including fan delta plain,fan delta front and fore fan delta,and further divided into some microfacies including distributary channel on water,back marsh,underwater distributary channel,inter distributary channel,sheet sand and so on;the sedimentary characteristics of the microfacies were detailedly explained.