Research Of Viscoelastic Reverse Time Migration Based On Q-Compensation

Migration is the key technique in seismic exploration,RTM(reverse time migration)became a research hotspot recent years because of its advantage on improving the complex structural reservoir imaging.Attenuation effect caused by anelastic properties of the subsurface media always exists in seismic data during the exploration.Especially high-attenuation areas could lead to poor data sets,which affects the useful information and would degrade the resolution of migrated images.Better migration methods need to be developed to deal with the anelastic effects in real rocks.To consider the absorption of energy and phase distortion of seismic waves,the Q compensation RTM could get higher migrated images and is helpful for seismic processing and interpretation,which can solve more complex exploration problem.Therefore,to mitigate the amplitude attenuation and phase dispersion effects in source and receiver wavefields can compensate the attenuation effects during the migration,which could produce higher resolution images.Based on constant Q model,a new modeling algorithm through fractional derivatives is introduced,to model seismic wave propagation in viscoelastic media based on spatial derivatives,specifically Laplacian differential operators of fractional order.An example shows that constant Q viscoelastic wave equation could describe the constant-Q attenuation and velocity dispersion behaviour.Recorded P and S waves in attenuation media face two important problems with multicomponent seismic data and high attenuation effect.Elastic RTM based on Fourier pseudospectral method is been used to migrate multicomponent data.The source and receiver wavefields are separated int P-and S-waves using divergence and curl operators before using image condition in RTM,which output PP,PS,SP and SS images provided more information and with less noise.From the energy conservation principle,and energy norm imaging condition is introduced in stress-velocity elastic wave equation for RTM.Numerical experiments show the quality of the imaging condition in attenuation backscattering artifacts.The advantage of compensation viscoelastic RTM is analysized,then formulating new propagation operators based on decoupled attenuation property of the viscoelastic wave equation to find the operator which is suitable applying in compensation viscoelastic propagation.Only phase correction and only amplitude compensation could be observed through the new operators modeling.Phase correction viscoleatcic propagation operator could correct the phase as needed and amplitude compensation propagation operator could amplify the amplitude,although with high frequency noise which can be suppressed using a filter.The whole workflow of Q compensation viscoelastic RTM is discussed,upon the operators proposed before different phase delay and amplitude compensation operators are chosen to apply in RTM based on cross-correlation imaging condition.At last,separating P-and S-waves during wavefield propagation with phase delay and amplitude compensation is introduced compensation viscoelastic RTM.Synthetic examples determine the ability of viscoelastic RTM to get more accurate images.The highlights of this dissertation:1)This thesis develop a elastic RTM method based on energy norm imaging condition.Numerical experiments show the effectiveness of method in backscattering artifacts attenuation.2)This thesis propose the new way of formulating viscoelastic propagation operators.The operaters can be used to correct phase and compensate amplitude during wave equation propagating in viscoelastic media for viscoelastic RTM based on Q.3)This thesis develop a viscoelastic RTM method based Q compensation.Both problems of migrating seismic record in viscoleastic media,include multicomponent data complexity and high attenuation effect,have been considered during this method.The advantage of phase correcting and amplitude compensation in migration images is been proved through numerical experiments.