Building tilted transversely isotropic depth models using localized anisotropic tomography with well information
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Published:2010-07
Issue:4
Volume:75
Page:D27-D36
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ISSN:0016-8033
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Container-title:GEOPHYSICS
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language:en
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Short-container-title:GEOPHYSICS
Author:
Bakulin Andrey12, Woodward Marta12, Nichols Dave12, Osypov Konstantin12, Zdraveva Olga12
Affiliation:
1. WesternGeco/Schlumberger, Houston, Texas, U.S.A.. 2. Formerly WesternGeco/Schlumberger; presently Saudi Aramco, Dhahran, Saudi Arabia..
Abstract
Tilted transverse isotropy (TTI) is increasingly recognized as a more geologically plausible description of anisotropy in sedimentary formations than vertical transverse isotropy (VTI). Although model-building approaches for VTI media are well understood, similar approaches for TTI media are in their infancy, even when the symmetry-axis direction is assumed known. We describe a tomographic approach that builds localized anisotropic models by jointly inverting surface-seismic and well data. We present a synthetic data example of anisotropic tomography applied to a layered TTI model with a symmetry-axis tilt of 45 degrees. We demonstrate three scenarios for constraining the solution. In the first scenario, velocity along the symmetry axis is known and tomography inverts for Thomsen’s [Formula: see text] and [Formula: see text] parame-ters. In the second scenario, tomography inverts for [Formula: see text], [Formula: see text], and velocity, using surface-seismic data and vertical check-shot traveltimes. In contrast to the VTI case, both these inversions are nonunique. To combat nonuniqueness, in the third scenario, we supplement check-shot and seismic data with the [Formula: see text] profile from an offset well. This allows recovery of the correct profiles for velocity along the symmetry axis and [Formula: see text]. We conclude that TTI is more ambiguous than VTI for model building. Additional well data or rock-physics assumptions may be required to constrain the tomography and arrive at geologically plausible TTI models. Furthermore, we demonstrate that VTI models with atypical Thomsen parameters can also fit the same joint seismic and check-shot data set. In this case, although imaging with VTI models can focus the TTI data and match vertical event depths, it leads to substantial lateral mispositioning of the reflections.
Publisher
Society of Exploration Geophysicists
Subject
Geochemistry and Petrology,Geophysics
Reference19 articles.
1. Audebert, F. S. , A. Pettenati, and V. Dirks, 2006, TTI anisotropic depth migration — Which tilt estimate should we use? 68th Conference & Technical Exhibition, EAGE, Extended Abstracts, P185. 2. Bakulin, A., M. Woodward, D. Nichols, K. Osypov, and O. Zdraveva, 2009a, Localized anisotropic tomography with well information in VTI media: 79th Annual International Meeting, SEG, Expanded Abstracts, 221–225. 3. Bakulin, A., M. Woodward, D. Nichols, K. Osypov, and O. Zdraveva, 2009b, Anisotropic model building with uncertainty analysis: 79th Annual International Meeting, SEG, Expanded Abstracts, 3720–3724. 4. Integrated velocity model estimation for improved positioning with anisotropic PSDM 5. Červený, V., 2001, Seismic ray theory: Cambridge University Press.
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