Prestack Reverse-time Migration And Imaging

In the field of seismic exploration, seismic migration imaging technology has been a hotspot and difficult problems.In recent years, with the development of seismic exploration, the target becomes more and more complex, which leads to a higher demand for efficiency and accuracy in seismic migration technology.The traditional migration methods are calculated by the depth extrapolation, and the wave theory based on one-way wave equation; Reverse time migration is extrapolated on the timeline, and the wave theory based on two-way wave equation. The use of full-wave equation, which allows wave propagation along each direction, so the media angle is not restricted and it can use in any model of speed changing.RTM can handle the model such as vertical and horizontal velocity changing, prismatic wave, turning wave multiples, etc. and the imaging result of complex structural is improved obviously, which the tradition one-way wave method scan not achieve. RTM mainly includes wave field extrapolation and imaging denoising .The reconstruction of reverse time wave fields is the key point that materializes the high accuracy of RTM. This thesis deduced the wave exploration operator under the rule-grid high-order finite difference forms of 3D wave equation, and analyzes the stability and frequency dispersion. This thesis also research the random boundary condition and storage problems based on the previous research result, and do some modification in the process of conventional RTM exploration.Getting the right image in the application of imaging condition is the direct influence imaging quality and precision. Conventional cross-correlation conditions will produce strong low frequency noise in model boundary surface and affect the imaging precision above the interface. This thesis firstly analyze the generation principle of imaging noise and introduces some denoising methods, then use a Laplacian filter to some models, and it can remove the low wave-number noise efficiently without reducing the accurate of the image. This thesis firstly introduces the principle of migration and traditional methods. Second, analysis and derivation each specific problem in the wave field exploration and imaging of RTM. Finally, complete prestack reverse-time migration of some models through the program, denoising to the results and have a compared with one-way wave method. The results is as follows: RTM need huge storage place and hve low calculation efficiency , random boundary conditions can solve the storage problem of RTM ,it is the most suitable boundary conditions for RTM ; The noise above the interface which generated by RTM of two-way wave equation can be eliminated effectively by Laplace operator; Compared with traditional migration, RTM is not affected by the imaging dip limit, could be properly imaged by the complex velocity structural, so it has a good future in practical application.