Study On Sedimentary Microfacies And Sedimentary Model Of Tide-dominated Estuaries In U Layer Of Block M In Ecuador

The research area is located in the Oriente Basin of Ecuador,South America.Previous studies on sedimentary models of the Cretaceous Napo Formation mainly have three mainstream views: tidal-dominated estuary-shelf sedimentary model,river-delta-shelf sedimentary model,and tidal flat-shelf sedimentary model.At present,there is a high recognition of the tidal-dominated estuarine-shelf sedimentary model,but there are still certain limitations in the exploration and development of oil and gas in the study area.On the basis of fine analysis of core in this study,combined with thin section identification of glauconite particles in the study area,associated pyrite and rosette shape under scanning electron microscope,it is indicated that it is developed in a weak oxidation environment and is of in-situ origin.At this point,it is believed that there is a transitional zone sedimentation between tidal-dominated estuaries and shelf sedimentation,similar to that between coastal sedimentation and shelf sedimentation.This provides a supplement to the sedimentary model of tidal-dominated estuaries towards the sea,and provides an important reference for the precise description and efficient development of oil fields of the same sedimentary type at home and abroad.Based on the theory of high-resolution sequence stratigraphy and sedimentology,this paper analyzes the core,logging and seismic data in the study area,based on the analysis of sedimentary characteristics of different levels of base level cycles and the identification of boundary characteristics of each level of base level cycle,the interior of the Napo Formation U layer in Block M of Ecuador is divided into 1 long-term base level rising half cycle,3mid-term base level cycles,and 7 short-term base level cycles.Based on this,a unified high-resolution sequence stratigraphic framework is established in the region based on short-term base level cycles.Based on core observation,logging,maturity analysis and microscopic thin sections of layer U,and by describing petrology characteristics such as core lithology and structure,as well as sedimentary characteristics such as sedimentary structure,biogenic trace fossils,sedimentary rhythm,and analyzing logging facies indicators,it is believed that layer U in the study area is developed in a tidal dominated marine continental transitional environment.On the basis of previous research,it is proposed that there is a transitional zone sedimentation between tidal-dominated estuaries and shelves,forming a tidal-dominated estuaries-transitional zone-shelf sedimentary system.A total of 7sedimentary microfacies have been identified,including tidal channels,tidal sand bars,sand flats,glauconite sand mat,mixed flats,shelf mud and gray beaches.Based on the analysis of sedimentary systems,a tidal-dominated estuarine-transitional zone-shelf sedimentary model was established in the study area.Based on the overall transgressive background of the Napo Formation U layer in the Oriente Basin,it is believed that the study area mainly includes three evolutionary stages: the MSC1 slow rising stage,the MSC2 fast rising stage,and the MSC3 fast falling and then rising stage.