Sequence Stratigraphy And Facies Of Fuyu Unit,Changyuan,Daqing Oilfield,Songliao Basin

Sequence and deposition of alluvial system are control by many factors,it’s quite difficult to study its sequence stratigraphy because its facies type and change.This thesis carries out the Fuyu unit to study the high-resolution sequence stratigraphy,explore the theory and basis of it in fluvial system.Application of the process-response principle,identify the changes o base level cycle by analyzing the characteristics of main geomorphic units in the process of A/S value stratigraphic response(stacking patterns)and sedimentary response(phase sequence and phase assemblages),and to establish multi-level base level cycle are an effective method of high-resolution sequence stratigraphy in alluvial system.Lots cores and well loggings shows that depositional type of Fuyu unit are fluvial and shallow delta system,the former can be subdivided into meandering and anastomosing river.Fuyu unit is overlay by the top conformity oilshale of Qingshankou Formation which can be a maker for correlation.Guided by the sedimentary theory of fluvial system,through the analysis of deposition of each facies in time sequence and apply of Wheeler diagram,the correlate method is built for channel,overbank,and paleosols.Identification of interfaces of base level cycle is based on the analysis of the sedimentological and stratigraphic responses of different structural units in fluvial system,such as channel,overbank and paleosols.Regional thick superimposed channel interval,extensive and regional mature red exposure paleosol,and regional thin sequence or minimum overbank sedimentation can be the maker of base level fall to rise,while thin isolated channel interval,thick and broad gray paleosol,and thick sequence or maximum overbank sedimentation can be the surface of base level rise to fall.The Fuyu unit can be divides into two 3-order and seven 4-order base level cycles.In consideration of palaeogeomorphology,source direction,well facies,Iso map of sandstone,width-thickness of channel,summarized that the fluvial channels evolve from the superimpose meandering channel,abandoned meandering channel,to regular meandering channel(FI3),meanwhile transited from upstream to downstream gradually and the anastomosing channel(FI2)eventually evolved into distributary channel(FI1)in shallow delta of lake margin as base level rise in Fuyu unit.This thesis is a theoretical basis for the establishment of sequence stratigraphic framework of the downstream fluvial system.The study of depositional system and evolution pattern in this framework,and summarized its evolutional model,all these gives a theoretical guidance and scientific basis to the exploration and development of petroleum in fluvial reservoir.