Prestack Full Waveform Inversion Method Research

With the increasing complexity of the oil-gas exploration, FWI (Full WaveformInversion), whicht reflects the objective laws of seismic wave propagation and can beapplied to arbitrary geological models, has become the focus of attention. However,because of the expensive computation and storage cost, FWI has not been put intopractice yet. Recently, with the development of the computer technology, FWI hasbecome a hot issue for geophysicists.In this thesis, several studies have been carried out for pre-stack FWI. A deepanalysis of the FWI theory is made and an integrated system is present. The major workand results achieved in this thesis are as follows:1. A detailed deduction of FWI in the acoustic approximation is made based onperturbation theory, and the flow chart of conjugate gradient method based FWI ispresent;2. The reverse-time propagation formula of the residual wave field based on PMLcontained staggered-mesh high-order finite-difference method is reduced, and both thestructure of the PML used here and the flow chart of reverse-time propagation ispresent;3. The linearized estimation of iteration step under the objective function in thisthesis is reduced;4. An analysis of the difference between the elimination of direct wave in FWI andthe migration imaging is made, and the method of direct wave elimination in FWI ispresent;5. An analysis of the generation of noise between layers is made from the angle ofwave propagation, and the eliminating method based on EPS(Edge PreservingSmoothing) is present;6. A logarithmic normalization method is presented for the problem that theparameters cannot update efficiently at the same time because of the huge differencebetween the order of magnitude, and the calculating formula of the dual perturbationunder the logarithmic model is present; 7. The MRNC (Model Reference Nonlinear Control) method for inversion processcontrol presented by Shi is used, which obtains satisfactory results within less iterationthan the traditional iteration step calculation method, and some transform of the originalformula is made to evade the computation of the Jacobian matrix;8. The FWI software module is established，and the core code is finished. Someexperiments on several typical geological models are made, and the results aresatisfactory.