Division,Correlation And Application Of Sequence Stratigraphy In Braided-river And Meandering-river Systems

Fluvial reservoir is one of the most important petroleum reservoir types in inner basin of Mesozoic and Cenozoic formation in China,and it is hard to study with the application of sequence stratigraphy.Based on former results,together with core,outcrop,well-logging and seismic data,this dissertation tries to propose a scheme for sequence stratigraphic division and correlation in braided-river and meandering river systems.Applying this scheme in actual regional to check its performance.This dissertation makes a conclusion for sequence stratigraphic respond characters,mainly shows in controlling base-level position,sand-body stacking patterns and distribution,litho-facies and fluvial style,under the conditions of changing A/S(Accommodation and Sediment Supply)within braided-and meandering-sediment.Meanwhile,this dissertation proposes an approach named A/S interval quantization principle based on consist and changing of litho-facies.Every litho-faces are numbered in idealized sedimentary profile,and through which the profile has been divided into two trend parts,largen or lessen upward.This principle defines the ratio of the litho-face number to bottom litho-face as A/S data in one trend part.Dividing short-term cycle with A/S data has well performed with classic theory,and leads to A/S research from qualitative to quantitative.Besides cycles are divided with the help of Fluvial Hierarchical Elements analysis.Within that analysis channel complex and floodplain make 5th sequence,and set the bottom of the channel complex as the sequence boundaries(short-term cycle surfaces).4th sequence stratigraphy(mid-term cycle)is divided with vertical character and stacking style of 5th.And their surface is used to make sequence stratigraphic framework to stratigraphic correlation.Mid-channel bar is the main body of braided river,and channel-filling formed by multiple bar,channel complex can be seen.Together with overlying floodplain form 5th sequence stratigraphy.So braided sequence stratigraphic base level should choose abandon surface of large profile sediment,and the abandon surface of braided channel within the same sequence should be parallel or nearby parallel.Due to meandering channel's isolated distribution,stratigraphic correlation applies equal altitude from datum as the same term-channel principle,and the upper fine sediment forming in relative stable condition should be chosen as the datum.Taking fluvial sediment of Guantao formation in Kendong as an example to study fluvial sequence stratigraphy.Guantao formation has been divided into two parts,braided sediment in lower part and meandering sediment in upper part.Applying the fluvial sequence stratigraphic research scheme proposed in this dissertation,Guantao formation n main wells is divided into 10-15 short-term cycles,5 mid-term cycles.Based on mid-term cycle in 11 wells,we make sequence stratigraphic framework to correlate stratigraphy within Guantao Formation in two orientations,W-E and SsN.From which we can get a conclusion that,lower braided channel accumulation and stacking together with wide distribution,which upper meandering channel isolated with strain distribution.Practice shows that it has more practical than classic sequence stratigraphy to apply the plan this dissertation proposed.