Application Research Of Tomography Velocity Modeling Based On Common Reflection Surface

With the continuous expansion of oil and gas exploration and development market at home and abroad and the increasingly severe international oil situation,complex areas such as mountains and deserts have become the focus and difficulty of oil and gas exploration and development,while deep oil and gas exploration has increasingly become the focus of attention of geophysical experts and scholars at home and abroad.However,in the above two cases,the effective data of the seismic data is weak,the signal-to-noise ratio is relatively low,and the high-quality imaging of the data is difficult.The common reflection surface stack and CRS tomography velocity modeling method can not only improve the signal-to-noise ratio of data,but also solve the velocity modeling problem caused by the difficulty of identifying weak signal coaxial.It has high application value in low signal-to-noise ratio data exploration and deep oil exploration.The theoretical basis of Common Reflection Surface(CRS)stacking is geometric seismology.The data are stacked based on the three parameters of normal seismic wave.It considers the local features of the reflective layer and all reflections within the first Fresnel zone.CRS stacking can be used to fill missing seismic traces,regularize pre-stack data and improve signal-to-noise ratio.Thus,the reflection coaxial of the pre-stack gather after improving the quality has better continuity,is conducive to identification and tracking.Another key problem in seismic data processing and migration imaging is how to establish an appropriate velocity model.As the best known zero offset stacking imaging method,common reflection surface(CRS)stacking can also obtain the kinematic properties of NIP wave field.It contains information about the structure of the underground reflector,such as inclination and curvature,which makes it possible to perform velocity inversion using normal incident point wave(NIP wave).However,the research on CRS attributes in China is still at the stage of theoretical research,and there are no applied research examples.In this paper,tomographic velocity modeling method based on common reflection surface is used to fully verify its theoretical and practical application.The inversion process is summarized as follows.Firstly,CRS stacking is performed on pre-stack seismic data to pick up high-quality CRS attribute parameters as input for inversion;then,an initial model is established,with the reverse gathering point of NIP wave as the starting point for ray tracing,and the CRS attribute parameters are simulated forward along the ray path until the ground;according to the wave field attribute and the residual of the simulated attribute,the velocity update amount can be calculated.This velocity inversion method inherits the advantages of CRS stacking and has strong anti-noise ability.Moreover,the inversion speed is fast and the algorithm is stable.The final velocity model obtained by multiple iterations can be directly applied to prestack depth migration,and it can also provide high-quality initial model for other more refined velocity inversion methods.It is expected to provide a new solution and become a technical reserve for velocity inversion under low signal-to-noise ratio.It has certain research significance and engineering application value.