Iranian Journal of Geophysics

Iranian Journal of Geophysics

Adaptive forward amplitude versus offset in Vertically Transversely Anisotropic (VTI) Medium Using Integrated Rock Physics Modeling and Thomson Coefficients

Document Type : Research Article

Author
Zahra Aghaei Kheyrabadi
M.Sc.in Geophysics, Department of Applied Geology, Faculty of Basic Sciences, Kharazmi University, Tehran, Iran
10.30499/ijg.2025.515281.1690
Abstract
As the extraction of information about petrophysics and fluid content from near-field versus far-field variations has gained more importance in recent years, understanding the effect of shale anisotropy in near-field versus far-field is essential. The layered structure of clay minerals causes elastic anisotropy. Shales (even conventional shale samples) are often elastically anisotropic due to the alignment of anisotropic clay minerals with the bedding plane. This research aims to address this issue by presenting a method based on rock physics modeling and the use of Thomsen parameters for AVO analysis in VTI environments. In this study, the impact of shale anisotropy on amplitude versus offset (AVO) analysis at the gas sand/shale interface in the Kerman Formation has been examined. This issue is important because accurate AVO analysis can be effective in identifying hydrocarbon areas, but in many previous studies, isotropy in environments has been assumed, which may lead to errors. In this study, the amplitude versus offset analysis in a vertically transverse isotropic (VTI) medium has been examined. For this purpose, Thomsen's anisotropy parameters were calculated. Since the anisotropy of shale affects the results of amplitude versus offset analysis at the gas sand/shale contact in the Kerman Formation, we have evaluated the impact of shale on amplitude versus offset analysis in the Kerman Formation. The results showed that in an anisotropic environment, Class 1 AVO is identifiable, indicating the presence of hydrocarbons, whereas in an isotropic environment, no distinct trend is observed in the AVO class. Additionally, it was observed in synthetic models that the effect of anisotropy is more pronounced at larger angles. The innovation of this study lies in presenting a combined analytical approach based on rock physics modeling and Thomsen parameters for AVO analysis in an anisotropic environment, which goes beyond classical isotropy assumptions and can aid in improving the location of new drilling areas.
Keywords
Thomsen parameters, range versus offset, Kazhdumi formation, transversely isotropic medium

Subjects

Abedi, M. M., Riahi, M. A., & Stovas, A. (2019). Three-parameter normal moveout correction in layered anisotropic media: A stretch-free approach. Geophysics, 84(3), C129-C142.
Asaka, M. (2018). Anisotropic AVO: Implications for reservoir characterization. The Leading Edge, 37(12), 916-923. https://doi.org/10.1190/tle37120916.1
Bakulin, A. (2003). Intrinsic and layer-induced vertical transverse isotropy. Geophysics, 68(5), 1708-1713. https://doi.org/10.1190/1.1620644
Chopra, S., and Castagna, J. P. (2014). Investigations in geophysics—AVO. Society of Exploration Geophysicists, Tulsa.
Garnero, E. J., Moore, M. M., Lay, T., and Fouch, M. J. (2004). Isotropy or weak vertical transverse isotropy in D ″beneath the Atlantic Ocean. Journal of Geophysical Research: Solid Earth, 109(B8).
Grechka, V., Zhang, L., and Rector III, J. W. (2004). Shear waves in acoustic anisotropic media. Geophysics, 69(2), 576-582. https://doi.org/10.1190/1.1707077
Hampson, D. P., Russell, B. H., and Bankhead, B. (2005). Simultaneous inversion of pre-stack seismic data. In SEG Technical Program Expanded Abstracts 2005 (pp. 1633-1637). Society of Exploration Geophysicists.
Jiangbo, H., Jun, M., Jianli, W., Tongxing, X., & Chuanqi, L. (2025). Prestack reservoir prediction method in ray parameter domain based on wide azimuth ocean bottom node seismic data. Geophysical Prospecting, 73(3), 942-959.
Kim, K. Y., Wrolstad, K. H., and Aminzadeh, F. (1993). Effects of transverse isotropy on P-wave AVO for gas sands. Geophysics, 58(6), 883-888.
Li, Y. (2006). An empirical method for estimation of anisotropic parameters in clastic rocks. The Leading Edge, 25(6), 706-711.
Long, T., Chen, F., Han, D. H., Sun, M., McNease, J. D., & Zheng, Y. (2025). An experimental study of the anisotropic and dispersion signature of shale reservoirs: Implications for seismic well tie. Interpretation, 13(1), T59-T70.
Luo, C., Ba, J., and Carcione, J. M. (2022). A Hierarchical Prestack Seismic Inversion Scheme for VTI media based on the Exact Reflection Coefficient. IEEE Transactions on Geoscience and Remote Sensing, https://doi.org/10.1109/TGRS.2021.3140133.
Nye, J. F. (1985). Physical properties of crystals: their representation by tensors and matrices. Oxford university press.
Pan, X., Huang, L., & Liu, J. (2024). P-wave amplitude versus offset and azimuth and low-frequency anisotropic poro-acoustoelasticity. IEEE Transactions on Geoscience and Remote Sensing.
Rüger, A. (2002). Reflection coefficients and azimuthal AVO analysis in anisotropic media. Society of Exploration Geophysicists.
Sams, M., Nasseri, J., & Teng Hui Turm, S. (2025). Anisotropy estimation from deviated wells: uncertainties and their implications—A case study. Interpretation, 13(2), T247-T262.
Sayers, C. M., and Dasgupta, S. (2019). A predictive anisotropic rock-physics model for estimating elastic rock properties of unconventional shale reservoirs. The Leading Edge, 38(5), 358-365.
Simm, R., and Bacon, M. (2014). Seismic amplitude: An interpreter's handbook. Cambridge university press.
Thomsen, L. (1986). Weak elastic anisotropy. Geophysics, 51(10), 1954-1966.
Tsvankin, I., Gaiser, J., Grechka, V., Van Der Baan, M., and Thomsen, L. (2010). Seismic anisotropy in exploration and reservoir characterization: An overview. Geophysics, 75(5), 75A15-75A29. https://doi.org/10.1190/1.3481775
Wawrzyniak-Guz, K. (2019). Rock physics modelling for determination of effective elastic properties of the lower Paleozoic shale formation, North Poland. Acta Geophysica, 67(6), 1967-1989.
Yang, Y., Yin, X., & Li, K. (2025). Nonlinear amplitude variation with offset and azimuth inversion for horizontal transverse isotropic media based on the elastic stiffness matrix. Geophysics, 90(2), C15-C35.
Zhang, F., Wang, L., and Li, X. Y. (2020). Characterization of a shale-gas reservoir based on a seismic amplitude variation with offset inversion for transverse isotropy with vertical axis of symmetry media and quantitative seismic interpretation. Interpretation, 8(1), SA11-SA23.
Iranian Journal of Geophysics
Volume 20, Issue 1
March and April 2026
Pages 97-109