Study On Sequence Stratigraphy And Sedimentary Systems Of Yaojia Formation In Daqin Placanticline In Songliao Basin

The study area Daqing Placanticline, which is located in the Central Depression area of Songliao Basin ,is the most significant hydrocarbon exploration and production zone of Songliao Basin. The study interval Yaojia formation is one of the most important oil-bearing formations. Despite almost over half a century of hydrocarbon exploration and production, there has been a huge controversy over the sequence stratigraph and the depositional systems and of Yaojia formation. As such, the reestablishment of the sequence stratigraphic framwork and the examination of depositional systems and facies of Yaojiang formation is, both theoretically and pratically ,of great significance.First and foremost, based on seismic data,core,well logging,carbon and oxygen isotope,as well as paleontological materials, we identified and correlated sequence boundaries, the first flooding surface,the maximum flooding surface and high-frequency sequence boundaries .Afterwards,we established the synchronic framework of sequence stratigraphy of Yaojia formation and drew the conclusion that the Yaojia formation is a third-order sequence ,which is composed of LST,TST and HST, and that these system tracts can commonly be devided into three to four forth-order sequences.Then, within the synchronic framework of Yaojia formation, the kinds of depositional systems and facies were identified on the basis of core ,well logging data,and so on. The depositional systems developed include delta depositional systems,lacustrine depositional systems,as well as gravity depositional systems. These depositional systems comprise sedimentary facies as follows: delta plain,delta front, prodelta, shallow lake, turbidite and so forth.Besides, the provenance of Yaojiang formation was studied based upon the percentage content of Zircon ,the ZTR index ,the Stability Factor and sandstone percentage content.According to the research, we found that there were four provenances ,including the Northwest provenance,the Southwest provenance and the North provenance. Based on the results of the provenance study of Yaojiang formation and core, well logging,sandstone percentage content, colors of mudstone and some other materials,the evolution of depositional systems and facies of Yaojiang formation was analyzed.At last, based on the sequence stratigraphic analysis and facies within it , the essentials of hydrocarbon accumulation, including source rocks,reservoirs , cap rocks and the combination of them,were studied.Then, On the basis of the analysis of essentials of hydroncarbon ,combined with seismic structrual analysis, the favorable zones of hydrocarbon exploration in Sabei area of Daqing Placanticline was predicted as follows: during the period of LST and HST of Yaojiang formation, the Northern part and the Eastern part of this area are the most favorable hydrocarbon exploration area.