E3S Web Conf.
Volume 133, 2019AG 2019 – 5th International Conference on Applied Geophysics
|Number of page(s)||8|
|Section||Application of Geophysical Methods|
|Published online||25 November 2019|
VSP data inversion for vertical velocity gradient and elliptical anisotropy model
1 AGH University of Science and Technology, Department of Geoinformatics and Applied Computer Sciences, 30-065 Krakow, Poland
2 Husky Energy Inc., St. John’s, Canada
* Corresponding author: firstname.lastname@example.org
Inversion of velocity parameters for the walkaway VSP data in a multilayered medium can be impeded by velocity gradients and anisotropy in some layers. A problem occurs if we compare velocities obtained from borehole seismic profiling which are equal to their vertical components with the velocities calculated with paths coming from far offsets where the horizontal component plays an important role, especially when the vertical gradient exists and the ray paths are curve-shaped. In this contribution we present the results of velocity model inversion for VSP data considering velocity gradient and elliptical anisotropy. The algorithm consists of two steps, optimization of velocity parameters and optimization of ray paths for the given model. Both procedures use the Nelder-Mead simplex method which finds local minima. Due to the character of optimization we performed also multistart analysis which can provide information about possible equivalences between parameters. Analysis was conducted for different parameterizations, in some cases allowing introduction of additional parameters: vertical gradient and elliptical anisotropy coefficient. The optimal model for a specific set of data is chosen with the help of Bayesian Information Criterion to balance complexity of model with quality of approximation of traveltimes.
Key words: seismic method / elastic anisotropy / inversion / BIC
© The Authors, published by EDP Sciences, 2019
This is an Open Access article distributed under the terms of the Creative Commons Attribution License 4.0, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
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