| Based on the special oil and gas project "key technology for effective development of super heavy oil and oil sands in the Americas",the genetic mechanism and heterogeneity evaluation of large oil sand sandstone reservoir(task No.: 2016zx05031-002-001)are studied.The tidal estuary is controlled by both river and tide,and the reservoir development characteristics and formation factors are complex,which makes the exploration and development of the tidal estuary difficult.In this paper,the physical simulation experiment and numerical simulation method are used to simulate the reservoir of tidal estuary,revealing the origin,scale,shape and spatial distribution of sand bar,which lays a foundation for the reservoir prediction of the underground estuary.Through the collection of topography and hydrological data of Qiantang River Estuary,the key parameters of sediment simulation are determined.The spatial distribution of sand bar is obtained by interpreting the simulation results,and the applicability of sediment simulation method is determined by comparing with the sediment investigation of Qiantang River Estuary.On this basis,by setting different hydrodynamic conditions,bed slope and sediment content differences,the single factor and multi factor deposition numerical simulation are carried out respectively,and the changes of hydrodynamic force and bottom shape in different parts are observed,and then the formation mechanism and main control factors of sand bar are determined.The shape,scale and spatial distribution characteristics of the sand bar are determined by interpreting the results of the numerical simulation.The optimal hydrodynamic conditions,bed slope and sediment supply are obtained.Based on the optimal parameters,the similarity theory is adopted to design the experimental scheme of sedimentary physical simulation,which can further reveal the origin and distribution of sand bar.The results show that:(1)The narrow to wide channel shape from the river inlet to the river mouth determines the difference of hydrodynamic energy in each section of the tidal estuary,which leads to the difference of types of sand bars developed in each section.The width of the channel from Tonglu to Shupu is narrow,which is mainly affected by the river flow.The flow in this section is "S" shaped movement,so it is easy to develop point bars.From Shupu to Jinshan,it is Bedlo Ad convergence section(BLC section)is transformed by river flow and rising tide flow.The bed load carried by them is deposited in this section to form a U-shaped bar.The direction from Jinshan to the ocean is mainly affected by the tide.This section forms a long strip sand bar.From the land to the sea,Qiantang River successively develops point bar,Ushaped bar,composite bar and strip bar.(2)The development direction of the channel changes with the asymmetry of the hydrodynamic energy on the north and south sides.The sediments deposited in the bed,and the roughness of the South and north sides of the bed was different,which resulted in the change of the slope of the bed on both sides of the estuary,and the change of the asymmetry of hydrodynamic energy.The types of sandbars developed in each section were obviously different.(3)Under the control of single factor condition,the small hydrodynamic condition and medium hydrodynamic condition are favorable for the development of sand bar in the river,and the development speed of sand bar is fast.Under the condition of large hydrodynamic force,sediments are brought into the ocean,which is not conducive to the development of sand bars,and the development speed of sand bars is slow;when the bed slope is 0.002 °,the sand bars are retrograde,0.003 ° are vertical accretion and progradation,0.004 ° are progradation,and the bed slope results in the difference of sedimentation process;under the condition of small sediment content,the development scale of sand bars is small,and with the increase of sediment content,The phenomenon of sand bar superimposition and splicing is more obvious,the scale of sand bar becomes larger,and the elevation increases;under the control of two factors,the sequence of factors controlling the formation of sand bar in tidal estuary from strong to weak is as follows: the slope of bottom bed plays a leading role in the development of sand body,the hydrodynamic condition plays a second role in the development of sand body,and finally,the sediment content plays a controlling role in the development of sand bar.(4)The physical simulation experiment shows that the formation of sand bar is also controlled by hydrodynamic conditions,bed slope and sediment content.The influence of hydrodynamic conditions on flood channel and ebb channel is significant;the slope of the bed leads to the asymmetry of hydrodynamic energy to a greater extent.During flood tide,a diamond cutting surface is formed on one side of the flood channel,and another diamond cutting surface is formed on the other side of the ebb channel.The two diamond cutting surfaces will be spliced and overlapped with the experiment;deposition The material supply accelerates the balance between the channel growth and the sand bar development in the tidal estuary system.The concave bank of the channel on the eroded side of the sand bar is formed,and the convex bank of the channel is formed at the growth place of the sand bar.The elevation of the sand bar increases because the water carries sediment across the bar crest.(5)Combined with the numerical simulation and physical simulation,it is determined that the genesis and distribution of the internal sand bar are similar under the similar geomorphic form of the tidal estuary,and the hydrodynamic factors determine whether to develop the sand bar or not;the slope of the bottom bed determines the difference of the sedimentation process to a certain extent,the smaller the slope of the bottom bed,the suspended load will be transported to the far source end of the river,and it will sink throughout the river Product,which controls the macro heterogeneity.The influence of sediment content on the development of sand bar comes from the fact that sediment can accelerate the internal equilibrium of tidal estuary system,and at the same time,it dominates the elevation,scale and time limit of sand bar development. |
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