Dispersion And Attenuation Analysis Of Seismic Wave In Near-surface Viscoelastic Medium

For developing the methods of the unconventional oil and gas resources exploration,the first problem that should be solved is how to establish a mathematical-physical model that can describe the unconventional oil and gas reservoirs media.Therefore,the effect of the near-surface medium of the rich unconventional oil and gas region on the attenuation of seismic wave becomes asignificant problem that we need to study.Given the special geological conditions of the near surface of the unconventional oil and gas reservoirs,we choose D'Alembert model that is simpler and more effective than the other viscoelastic models,and it has the practical advantages.First,the dissipation coefficient of the Biot model is introduced into the D'Alembert model,so the original D'Alembert model is turned into the modified D'Alembert model that could give a good solution to its dimension mismatch between the left and right sides of the wave equation of the original D'Alembert media model by dimensional analysis.Meanwhile,the modified D'Alembert model couldalso describe the near-surface medium in the details through the multiscale.Numerical result shows that the predicted value of theattenuation of the modified D'Alembert model is close to the measured value of the near-surface medium.Second,viscoelastic skeleton moduli are introduced into the modified D'Alembert model to construct the improved near-surface viscoelastic model that combines the dissipation from solid-flow friction and the attenuation of the skeletal deformation.Numerical results showthe validity of the improved near-surface viscoelastic model,because the trend and values of theattenuation curve of the model are consistent with the measured attenuation curves of the near-surface medium.At last,to verify the advantages of the modified D'Alembert model and theimproved near-surface viscoelastic model in practical applications,the Biot model,the elastic BISQ model and the viscoelastic BISQ model are chosen to be compared with them.Numerical results show that the modified D'Alembert model and the improved near-surface viscoelastic model use fewerparameters(four and eightparameters)to get better fitting results than the other three models(ten,eleven and thirteenparameters).Therefore,the improved near-surface viscoelastic model and the modified D'Alembert model are useful to simulate the attenuation of the actual near-surface medium.