Wave-equation migration velocity analysis for VTI models

Abstract

Wave-equation migration velocity analysis (WEMVA) is a powerful technique for robust velocity model building when the subsurface is complex and the starting model is far from true. However, this traditional isotropic WEMVA technique cannot explain anisotropic wave phenomenon, which has significant effects when the reflectors are steeply dipping and/or the waves are traveling at large angles. Furthermore, errors in the anisotropic parameters cause similar defocusing as errors in isotropic velocity. Any defocusing caused by anisotropy may be translated to false updates in the isotropic velocity, which lead to further mispositioning and misinterpretations. However, simple extension of the isotropic WEMVA to the anisotropic medium cannot provide an unique and reliable solution due to the nonlinear and underdetermined nature of the anisotropic model building problem. Many anisotropic models with vastly different geological interpretations may explain the surface seismic data equally well. This thesis addresses these issues by including anisotropic effects in WEMVA and by integrating other useful information from geology and rock physics to better regularize the inversion. First, I extend the isotropic WEMVA method to the anisotropic medium to evaluate and update the anisotropic Earth models. Instead of the industry standard ray-based tomographic methods, the anisotropic WEMVA technique uses wavefields as information carrier to handle both the complex subsurface and the frequency-dependent behavior of the wave propagation. I include the geological information using steering filters to regularize the gradients. Both synthetic and field 2-D examples show that the anisotropic WEMVA technique can resolve the errors in both velocity and anisotropic parameters. Consequently, the migration images are vi

Image-guided wavefield tomography for VTI media

“…As suggested by Shan et al (2014) and Y. Li et al (2014), the objective function combines the differential semblance optimization (DSO) and image-power (IP) (Zhang and Shan, 2013) criteria:…”

Approximate Bayesian inference of seismic velocity and pore-pressure uncertainty with basin modeling, rock physics, and imaging constraints

“…Several authors have addressed the problem of incorporating geological and physical constraints in velocity inversion by employing basin modeling and rock physics (Petmecky et al, 2009;Brevik et al, 2011;Bachrach et al, 2013;Dutta et al, 2014;Li, 2014;De Prisco et al, 2015). Basin modeling presents a quantitative framework for simulating geologic processes through time and yields various earth properties such as porosity, pore-pressure, effective stress and mineral volume fractions (Hantschel and Kauerauf, 2009).…”

Automatic wave-equation migration velocity analysis by focusing subsurface virtual sources

“…The vertical transverse isotropic (VTI) (Alkhalifah, 1998) model is representative of the first-order anisotropy present in the subsurface. Several authors have used WEMVA in VTI media to build an anisotropic model based on the DSO method (Li et al, 2014;Weibull and Arntsen, 2014).…”