Multi-parameter Inversion Of VSP Based On Frequency Domain Viscoelastic Wave Equation

In the exploration and development of oil and gas fields,VSP which is a well seismic exploration method plays a role as a bridge connecting ground seismic,drilling and geological data.Using VSP data to obtain accurate elastic parameters and Q values will lay the foundation for later calibration of seismic geological formations,interpretation of results and prediction of oil and gas,and also provide reliable constraints for prestack inversion.Using the viscoelastic wave equation in the frequency domain for inversion,the VSP parameter model can be established to overcome the shortcomings of conventionally only using traveling time.However,using the conventional local optimization algorithm for the inversion of the wave equation,especially the simultaneous inversion of multiple parameters,it is easy to fall into the local extreme and the result is inaccurate.Therefore,this paper proposes a fast segmented simulated annealing(SFSA)algorithm with global optimization performance for inversion.The algorithm adopts strategy using different disturbance models and annealing methods in different stages.Compared with the conventional simulated annealing algorithm,this algorithm effectively improves the efficiency of the algorithm and converges to the optimal solution quickly.It can be used to increase the accuracy and efficiency of parameter estimation when using VSP data with a small amount of data.In seismic exploration,the modeling and inversion in complex media usually contain many parameters which reflect the different properties of the media.However,the simultaneous inversion of the five parameters of P-wave velocity,density and quality factor(Qp and Qs)is not satisfied.So in this paper,the feasibility of VSP multi-parameter inversion in frequency-domain viscoelastic wave equation is analyzed.The sensitivity of the five parameters to the objective function and the coupling between the parameters are clarified and a multi-parameter inversion method of the fractional-step VSP wave equation based on travel-time constraints is proposed.Firstly,we use VSP data to construct prior information,and then perform fractional frequency stepwise inversion,that is,the process of "three parameter inversion +five parameter inversion" to improve the robustness of inversion.In this paper,accurate elastic wave velocity,density and quality factor near the wellhead at the seismic band scale can be obtained at the same time,which lays a good foundation for precise time-depth relationship and hydrocarbon interpretation and prediction.Meanwhile,it provides reliable constraint for prestack inversion and enhance the reliability of seismic inversion.