Sedimentary Numerical Simulation Research Of Braided River Reservoir In Guantao Formation,Yangerzhuang Oil Field,Haunghua Depression

Braided river is an important type of river pattern and one of the major types of oil and gas reservoirs.It is widely developed in the Mesozoic and Cenozoic continental petroliferous basins in China.Researches about facies model and reservoir architecture of braided river has been reported in many literatures at home and abroad.However,there are few studies on the forming processes about the main sediments in the braided river such as braided bar,and no unified view has yet been formed.In this paper,Yangerzhuang Oilfield in the southern part of Huanghua Depression is used as the study area.The typical braided river sediments of the Neogene Guantao Formation are selected.Based on the study of sedimentary microfacies and the internal structure of braided bar,the method of sedimentary numerical simulation is used to explore the formation process of microfacies unit such as braided bar.The braided river sand body in the study area is widely developed.Based on the regional sedimentary background,the core,logging and development dynamic data are combined to study the sedimentary microfacies and internal structure of the dense well network area.The evolution of single channel and the distribution and internal structure of the braided bar is analyzed.The study shows that there are four superimposed relationships in the sand body in the section.The superposition method evolves from the small area superposition and layered superposition in the lower part of Ng III and Ng II to the small layered superposition and isolated in the upper part of Ng II and the bottom of Ng I.In the upper part of the Ng I section,as the sedimentary environment changes,the superposition method of sand body gradually evolves into big area superposition and layered superposition.On the plane,sand bodies in the main layer distributes continuously in a large area.The sedimentary range of the mud stone in the flood plain facies is small,and the river channel filling sedimentation forms local seepage barriers;falling silty seams develop inside braided bar,and its shape and distribution range are limited.Channel filling sedimentation and braided bar in the single braided belt make braided river reservoir complicated.In order to understand the formation process and development law of the river channel and the braided bar in the study area,the fluid hydrodynamics-based Delft 3D software is choosed.The key parameters of sedimentary numerical simulation are determined by core particle size analysis data,paleotopography restoration data,and the hydrological data of modern braided river which is similar to the braided river in the study of reservoir sedimentary facies.Based on the parameters determained by actual data from underground reservoir in the study area,the sedimentation process of braided river in the study area was simulated.The developmental characteristics of different types of braided bar and braided waterways are emphasically analysed.The statistics of the development scale of the braided bar show that the simulation results are in good agreement with the results of the dense well network area.The effects of slope,grain size of sediment,river flow,sediment concentration and water level on the braided river sedimentation were discussed through the sediments simulation of braided river under different conditions.The study shows that,progradation,lateral accrection,vertical accrection,and erosion together shape the shape of the braided bar and its internal structure.Progradation and vertical accrection control the planar and vertical growth of braided bar,and cause the merger of different braided bars;lateral accrection,and erosion jointly control the lateral migration and asymmetric growth of the braided bar.The periodic hydrodynamic change of river sediments controls the coupling of the above effects,forming the deposition of falling silty seams,the development of gullies at the top of the braided bar,and the division and merger of braided bars.Guided by the understanding of sedimentary model,the development and evolution process of the braided bar in braided river reservoir in the detailed case study area was analyzed,and the sedimentary evolution model of the detailed case study area was established.The results of this thesis provide a geological basis for the fine development and adjustment of the braided river reservoir in Yangerzhuang Oilfield,and provide scientific understanding for the genesis and evolution of key sedimentary bodies in the braided river especially braided bars.