High resolution sequence stratigraphy in fan delta facies:A case study from Upper Karamay Formation reservoir in Bai-21 well area in Karamay Oilfield

In order to recognize the characteristics of fan delta facies reservoir and improve the reservoir description accuracy,this paper carried out the study on the reservoir of Upper Karamay Formation based on high resolution sequence stratigraphy and the strata cyclicity as well as sedimentology response caused by different grade base level change.The Upper Karamay Formation in Bai-21 well area can be divided into one long-term sequence cycle,two middle-term sequence cycles,14 short-term sequence cycles and 33～37 super-short-term sequence cycles.The short-term sequence cycles can be divided into two basic structure types which are up-deepening asymmetry and up-shallowing asymmetry.The sedimentary sequence,structure type,stacking pattern and distribution pattern of super-short-term sequence cycles in the process of base level change were discussed in detail.The sequence stratigraphic framework was built up by making short-term sequence as isochronous stratigraphic correlation unit.The sedimentary characteristics of sand body and the oil-gas distribution were analyzed.All these studies provide a good foundation for reservoir research and later development of Upper Karamay Formation in the Bai-21well area.