Amplitude-Preserved Migration With Viscoelastic Wave Equations

The study on amplitude-preserved migration for imaging complex media in the crust has become a frontier technology in petroleum exploration and production nowadays. Thus, the amplitude-preserved imaging methods, which are based on viscoelastic wave equations, are getting more popular and expected to sever as routine seismic processing tools in the near future. In this thesis, techniques for processing of seismic data, including 2D and 3D pre-stack amplitude-preserved depth migration with viscoelastic wave equations, parsimonious kirchhoff integral pre-stack depth migration and Multi-scale curvature analysis with wavelet transformation, are presented.Conventional pre-stack migration based on the scalar wave equation compensates for geometrical spreading, but it does not do for transmission losses, intrinsic Q losses, and dispersion. Thus, the main objective of this thesis is to develop a amplitude-preserved pre-stack depth migration method based on viscoelatic wave equations. As the first step, 2D and 3D preserved-amplitude pre-stack depth migration algorithm with viscoelastic wave equations are developed in chapter 3 and in chapter 4. The required corrections are performed during the pre-stack migration that uses a viscoscalar, one way, depth-stepping wave equation for extrapolation of both source and receiver wavefields in the frequency-space domain. The Q compensation is performed with including a Q-dependent term in the extrapolation. Dispersion is corrected using a frequency-dependent velocity model. At the same time, the imaging condition is modified to provide a correction to the propagating source and receiver wave fields at each depth step to compensate for transmission losses. Good processed results of Synthetic data and real seismic data have proved that this algorithm is stable, reliable and widely applicable.Kirchhoff integral for 3D PSDM has three advantages. First, it is suitable to seismic data collected in any irregular survey. Second, target oriented imaging makes it easy to define migration targets for sub-volume imaging or CRP gathers, even for full volume data. Third, it is of high computational efficiency. It is particularly useful migration velocity analysis. These points show that it is indispensable kind of migration algorithm. As the second step, such an approach to parsimonious 2-D Pre-stack kirchhoff Depth Migration is developed in chapter 5. Using this method fast computation can be obtained in seismic data processing. Thus, this method can be used for migration velocity analysis, in-site data process on a workstation and the migration quality control。The 3D PSDM is a systematic processing flow in both theory and application. In the flow, each step directly affects imaging results. In order to get good processing results of 3D pre-stack depth migration, such an migration processing flow is developed in chapter 6. Using this workflow one can gain good results of 3D pre-stack depth migration. First of all, the author summarizes the key questions of 3D pre-stack depth migration process; then, analyzes how to deal with those problems; finally, a 3D PSDM processing flow chart is presented. This workflow can be used to supervise 3D PSDM processing.Interpretation faults are very difficulty in complex structure areas. In order to get good interpretation results, the author combine geological, geophysical and rock mechanics approach to natural fractural reservoir characters. The local Multi-scale curvature analysis with wavelet spectrum decomposition on 3D seismic data is presented to detect distributions of fault and sub-fault systems in chapter 7. Based on this approach and using 3D seismic data, extracted frequency dependent curvature attribute cubes and curvature attributes mapping provide an efficient tool to delineate distributions of reservoirs and fault systems. Good processed results of real 3D seismic data have proved that this algorithm is stable, reliable and widely applicable.