Two-dimensional Joint Inversion Of Marine Controlled-source Electromagnetic And Seismic Full-waveform Method

Joint inversion is an approach which uses various types of geophysical data,through the mutual constrains between model parameters to recover the models satisfied with multi-geophysical data set.Joint inversion overcomes the shortcomings of separate inversion because of its great improvements in reducing the limitations and the ambiguity of inversion problem,and in the inversion results.Full waveform inversion can provide high-resolution images of geological structure,but it is difficult to identify fluid properties such as oil-water interface.Marine controlled-source electromagnetic(CSEM)effectively distinguishes the electrical difference,however,its vertical resolution is low because of the skin effect.Therefore,how to take the complementary advantages of the two methods,realize joint inversion of resistivity and velocity via the theory of cross-gradient,and improve the inversion accuracy is the emphasis of our study.Frequency-domain seismic full-waveform forward adopts the finite-difference method discretized by the so-called 9-point mixed-grid approach,and the gradient method and single-frequency sequential inversion are used,which restore well the characteristics of the anomalous body.Finite element method based on quadrilateral meshes is applied for solving the forward problem of marine CSEM,and data space inversion derived from model space through mathematical formulas is used to invert resistivity.This method can reduce computer memory consumption and enhance the efficiency of calculation.Introducing the cross-gradient function achieves the physical structure of two kinds of mutual coupling,and finally a marine CSEM and seismic full-waveform two-dimensional joint inversion algorithm is successfully developed.Theoretical model data including tabular,prism,groove and complex body are tested by the inversion algorithm described above,whose results demonstrate that the joint inversion method compared with the separate can better recover the anomalous body form space,structure as well as property values,so as to verify the validity of the 2-D joint inversion.