Discussion Of Division Method Of Fluvial Sequence Stratigraphy

Fluvial facies reservoir is one of important reservoirs in Meso-Cenozoic continental basin in China. It is necessary to discuss the research method of sequence stratigraphy for fluvial facies reservoir evaluation and prediction. For Daqing Placanticline, there is no unified sequence division scheme because of poor research of sequence stratigraphy and sedimentary systems for the whole area. Based on recognizing types of sediment micro-facies, the paper discuss division method of sequence stratigraphy for fluvial facies, and using it to establish time-equivalent stratigraphic framework.Combining regional tectonic and sediment background、former research result、core observation and well logging, meandering river、anastomosed river and shallow delta sedimentary systems can be identified in Fuyu oil-bearing layer. The micro facies in meandering river include meandering channel、crevasse channel、crevasse splay、floodplain and interchannel lacustrine; microfacies in anastomosed river include anastomosed channel、crevasse splay complex and floodplain; distributary channel、interdistributary bay、underwater distributary channel、mouth bar、sheet sand and underwater interdistributary mud.Guided by high resolution sequence stratigraphy theory and fluvial sedimentology theory, based on analyzing types of sedimentary faceis and facies association, illustrated identification sign of base-level cycles alternation through identifying sedimentologic and stratigraphic responses of fluvial sub-facies with different A/S ration, including turnaround surface identification sign of ascending to descending and descending to ascending of base-levels. Based on this, the paper identified key surfaces of middle cycle of base-level. There is an unconformity in F1.3, so the whole Fuyu oil-bearing layer could be two long-term cycle, and five middle-term cycles.Fluvial subfacies (microfacies) sequence correlation method is discussed within sequence stratigraphic framework. Synchronizing channel could be correlated through equal elevation method, as this, asynchronous channel could be identified. Based on recognizing sedimentary facies correctly, using fluvial sedimentary principle to analyze sedimentary relationships of channels、crevasse splay and floodplain, confirming time correlation relationship through Wheeler illustration, correlate method of base of channel and crevasse splay and floodplain can be proposed. Forming a suit of sequence stratigraphy unit division and correlation thinking and technique, and using this technique in Fuyu oil-bearing layer, one scheme of Fuyu oil-bearing sequence stratigraphy division can be established.Feature of channel distribution identified by single well and well tie, combining structure、palaeogeomorphology and direction of resource, sandbody distribution synthetical geologic prediction research have been done. This paper analyzed distribution of sedimentary system and evolution feature of Fuyu oil-bearing layer in each unit of middle-term cycle. Research shows that Fuyu oil-bearing developed in a process of base-level ascending and accommodation increasing upward, and the depositional system transformed from meandering river to anastomosed river to shallow delta.