Density plays an important role in hydrocarbon interpretation and it can predict fluid saturation of reservoir. Due to the cross-talk effects between velocity and density, density is difficult to reconstruct in multi-parameter full waveform inversion. FWI, especially multi-parameter FWI, is an ill posed problem and has a strong dependence on the initial models. Based on the analysis of the influence of density and velocity on wave propagation and model test, we discover that density inversion result grows desirable while misfit of the initial velocity goes down slightly. Therefore, looking for the methods to establish a suitable initial model is very important for improving the accuracy of the inversion results of density. AVO (Amplitude Variation with Offset) technology is a new exploration technique using the relationship between seismic reflection amplitude and offset for searching oil and gas. AVO inversion can get well velocity result. But for density, the result is unsatisfactory because the density is not sensitive to the change of amplitude. But it's enough to be the initial model for FWI. So we propose a new method for inversion. That is joint AVO and multi-parameter FWI. The numerical examples testify the feasibility of our method.
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