Sedimentary Evolution And Fine Architectural Analysis Of Braided To Meandering Fluvial Reservoir

Fluvial reservoir is an important carrier of petroleum resources in China.Most of the old oilfields in eastern China have been faced with problems such as: high comprehensive water content and great difficulty in stabilizing production.Quantitative architectural reservoir characterization can provide an important basis for judging the connectivity of sandbodies and fine geological modeling.This paper takes the fluvial facies reservoirs in upper Guantao Formation in Block 6 of the Gudong Oilfield as the research object.Integrated use of the core,wireline log,seismic cube,modern rivers,and literature data,the fluvial types,evolutionary model,and controlling factors of the fluvial style change in the upper Guantao Formation was studied.Based on core and wireline log,the characteristics of different levels of architectural elements and interfaces were analyzed,and the fluvial architectural model was built.Under the control of the dense array of well and the statistical formula from the modern fluvial geomorphic parameters,the distribution scale of different architectural element can be characterized quantitatively,and the fluvial architectural parameters database of upper Guantao Formation in Block 6,Gudong Oilfield was established.Combined with the development porportion of different lithofacies in each architecture units,the development characteristic of small-scale architectural elements were characterized quantitatively.Through the observation of the core in the sealed coring wells,the typical lithofacies,lithofacies combination,and architectural elements were identified.The logging identification templates of different sedimentary microfacies were established by using the calibration of log and core.The seismic cube was inverted based on the SP log,and the well-seismic combination guides the layer correlation and the sandbody stacking patterns.Furthermore,the sandbody isopach maps in each layer were guided by the horizontal seismic slices.Based on the regional geological background,core,well logging,seismic geomorphology,and sandbody isopach map distribution,it is believed that there are braided rivers and meandering rivers developing in the upper Guantao Formation,and the the braided to meandering fluvial evolution model was establised.The control factors of tectonic movement,paleo-climate,and lake level changes on the fluvial style change were discussed.Through the lithology and log calibration of the coring wells,the sedimentary characteristics of the architectural elements and the logging curve characteristics of the architectural interface in different levels are clarified,and the hierarchical architectural model of the fluvial facies reservoir of the upper Guantao Formation in Block 6 of the Gudong Oilfield was clarified.Based on sedimentary characteristics in the core,the sedimentary characteristics different architectural elements were explained.Under the guidance of fluvial facies deposition models,combined with modern river geomorphic styles and sandbody isopach map,the braided and meandering fluvial microfacies distribution on the plane was completed.Under the guidance of microfacies,the horizontal and vertical splicing patterns of different architectural elements in fluvial reservoirs were summarized.Based on the modern meandering river geomorphology,outcrop,and subsurface reservoir seismic geomorphology,point bars are always downstream rotation and translation in the process of lateral migration,which can result upstream and downstream deviation angles.The geomorphological parameters of modern meandering rivers shows that there is a good correlation between the upstream deviation angle and the ratio of width and looplength,the upstream deviation angle and the downstream deviation angle.Under the condition of the bar length,width,and looplength are determined,the upstream and downstream deviation angle of the point bar can be calculated,and the location of the migration orientation point can be decided.The number and distribution of interlayers in the point bar are completed through the horizontal-section comparison under the dense well array control.This method can be used to quantitatively characterize the architecture of the rotation and translation style point bar.The development of the silt layer in braid bar can be identified using the well correlation by the leveling the bottom of the braid bar,and the dip angle of the head,tail,the wings of the bar can be computed.Through the geomorphological parameters statistics of multiple modern river sections,the relationship between different geomorphic parameters was analyzed.The established empirical formula of modern river geomorphological parameters was used to obtain the subsurface fluvial facies reservoir architectural parameters.Furthermore,a database about the fluvial architectural parameters was established,and a set of methods for quantitative characterization of reservoir architectural parameters was created.By counting the lithofacies thickness and the proportion of the different lithofacies in each architectural elements from the coring wells,the average development ratio of different lithofacies in each architectural elements of meandering and braided rivers was computed.Then the development ratio of different lithofacies units in the whole area and sandbody was analyzed.A set of methods for quantitative characterization of small-scale architecture was formed.Based on the parameter relationship between the width-length and width-thickness of the bar,and the development ratio of different lithofacies in the bar,the volume model of the bar and volume model of the different lithofacies were established.Based on the fluvial evolution and studies on the parameters of different fluvial types in the upper Guantao Formation of the Gudong Oilfield,the sedimentological response on the channel width and thickness,archictectural geometric scale,and lithofacies ratio were summarized.