The Study And Application Of Quality Factor Extraction Method Based On VSP Data In Frequency Domain

The propagation of seismic waves in the actual earth medium is affected by the inelastic properties of the strata,the rock skeleton and the pore fluid properties,resulting in the dispersion of the seismic wave velocity and the amplitude and energy attenuation.Among them,the seismic attenuation characteristics caused by the viscoelasticity of the medium are usually characterized by the formation quality factor Q,which is more sensitive than the seismic velocity in reflecting the fluid properties.Therefore,it is of great significance to improve the accuracy and stability of quality factor extraction to seismic energy compensation,improve the resolution of seismic data,carry out reservoir prediction and oil and gas identification.At this stage,the spectral ratio commonly used is susceptible to the influence of factors such as window,band selection and direct division of spectrum,which limits the accuracy and stability of the quality factor extraction results.Coupled with the current commonly used quality factor extraction method for the use of phase spectrum information is not enough,can not accurately and steadily extract the quality factor.Therefore,in view of the problem of accuracy and stability of conventional extraction methods,the paper uses the advantages of VSP seismic record,namely,information precision,resolution,credibility and more targeted to the reservoir in the frequency domain to carry out quality factor Research and Application of Q-value Extraction Method.The amplitude spectrum information of the frequency domain is one of the important signs to reflect the attenuation of the seismic wave.Based on the energy variation of the frequency domain before and after the interface of the dielectric domain,the minimum energy difference of the amplitude spectrum energy of the seismic wave amplitude energy with Q value is deduced The objective function of the quality factor extraction method is obtained by finding the optimal solution.Which effectively solves the influence caused by direct phase division and frequency band selection,and improves the accuracy of quality factor extraction.On the basis of this,considering the multi-scale characteristic of seismic data,the quality factor Q is extracted by using the low,medium and high frequency range,which greatly improves the stability of Q value extraction.Synthetic VSP data and actual seismic data test show that this method can effectively improve the quality factor extraction stability and accuracy.The frequency domain phase spectrum is important for measuring the energy attenuation in the process of seismic wave propagation.It is shown that the phase angle of the seismic wave shows a certain change with the frequency at a certain reference frequency.On this basis,the paper deduces the formula of extracting Q value by phase spectrum,and verifies the feasibility of the method by model.On this basis,the formula of extracting the Q value by the amplitude spectrum and the phase spectrum is further deduced,and the feasibility of the method is tested by synthesizing the VSP seismic data.