| In today’s oil and gas search,the accuracy of the imaging of underground structures is the key to the smooth progress of the work.The pre-stack depth migration imaging technology is widely used in industrial production,and the accuracy of the velocity model,especially in the middle and deep layers.The location is critical to the pre-stack depth migration algorithm.Conventional migration velocity analysis methods are not only inefficient and cannot meet the requirements of high-precision velocity inversion,especially in the shallow area of the velocity model.Therefore,it is necessary to apply a more accurate tomographic velocity inversion method.The traditional global grid tomography inversion method belongs to the reflected wave tomography.Although the velocity model can be inverted as a whole,the accuracy of the shallow velocity is far less than that of the first arrival wave tomography and ignores the accumulation of errors from shallow to deep layers.The anisotropy of the underground medium leads to inaccurate deep imaging.In addition,it is difficult to restore the original shape of the velocity model in the absence of horizon constraints.Although the anisotropic tomographic inversion method based on "layer stripping" can reduce the accumulation of errors,its inversion efficiency is also high.It greatly reduces and cannot fundamentally improve the accuracy of the shallow layer of the velocity model.For this reason,this paper proposes an anisotropic global travel time tomographic inversion method based on corner gathers,which can update the velocity model globally or update a certain target area individually,and invert the first arrival wave tomography with high precision in shallow layers.The velocity model is fused into the initial velocity model obtained from conventional velocity analysis,which improves the accuracy of the model and the efficiency of global tomography.Later,in the process of improved global tomography inversion,the sensitivity analysis of the Thmosen parameters based on the corner gathers is clearly defined.The range of small,medium,and large angle gathers;then use the velocity field after shallow,medium and deep fusion to perform reverse time migration,and use the optimized Poynting method vector to extract the angle gathers of the VTI medium in the process of reverse time migration,according to the degree of curvature of ADCIGs,the residual curvature is calculated to judge the accuracy of the velocity model.Before the target accuracy is reached,the accuracy of the velocity field improved by the global tomography is continued.The method in this paper improves the accuracy of the velocity model and improves the inversion at the same time.Efficiency,the trial calculation results of a simple model prove the correctness of the method,and the trial calculation results of a complex model prove the applicability. |
