Seismic Modeling, Inversion, and Imaging in Attenuating Media

Download or read book Seismic Modeling, Inversion, and Imaging in Attenuating Media written by Tieyuan Zhu and published by . This book was released on 2014 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Accurate seismic exploration demands sophisticated seismic techniques that can be applied to any complex geological setting, for example, attenuative and anisotropic media. This dissertation addresses attenuation problems in seismic exploration: how to model wave propagation in attenuating media, how to invert attenuation property of subsurface reliably, and how to mitigate attenuation effects in seismic images. The key innovations are (1) developing a novel viscoacoustic/elastic constant-Q wave equation that is practically efficient and accurately simulates the constant-Q attenuation behavior, (2) an iterative joint inversion framework for different geophysical datasets (e.g., attenuation data) to reduce the uncertainties of independent inversion results, (3) developing an Q-compensated reverse-time migration approach to compensate for attenuation effects (dispersion and amplitude loss) in seismic images. In the first part, I derive a novel viscoacoustic wave equation based on constant-Q theory. I investigate the accuracy of this wave equation. I show its application in a heterogeneous medium. Testing shows this model to be more computationally efficient than the most efficient single standard linear solid modeling. More importantly, this viscoacoustic equation separates attenuation and dispersion operators that allow us to mitigate both amplitude attenuation and phase dispersion effects in seismic imaging. This equation is the key modeling engine for seismic migration. Due to the data quality of the seismic waveform and the strong nonlinearity of the attenuation problem, I choose a joint inversion algorithm to invert for the attenuation coefficient. I develop an iterative joint inversion approach where one model domain acts as a constraint for inversion of the other, and the roles of the two domains are iteratively switched. This joint inversion stabilizes the inversion and ensures that results are geologically plausible. I apply the method to estimate Vp and the attenuation coefficient in field data examples. In the third part, I present a method to improve the image resolution by mitigating attenuation effects. I discuss the feasibility of time-reverse modeling in attenuating media using numerical experiments for 1D and 2D situations. I develop a Q-compensated reverse-time migration imaging approach (referred as Q-RTM). I illustrate this approach using different synthetic models. Numerical results further verify that this Q-RTM approach can effectively improve the resolution and quality of image, particularly beneath high-attenuation zones. To demonstrate the suitability, I apply the Q-RTM method to field data from the King Mountain site in west Texas. In the future, this method could readily be applied to other field datasets to improve the image resolution in high attenuation areas.