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Estimating fluid term and anisotropic parameters in saturated transversely isotropic media with aligned fractures

XINPENG PAN1,2 ,  GUANGZHI ZHANG2 ,  JIANXIN LIU1 ,  ZHENGYONG REN1*
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1 School of Geoscience and Info-Physics, Central South University, Changsha 410082, P.R. China.,
2 School of Sciences, China University of Petroleum (East China), Qingdao 266580, P.R. China.,
JSE 2021, 30(1), 65–84;
Submitted: 2 June 2019 | Accepted: 8 September 2020 | Published: 1 February 2021
© 2021 by the Authors. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution -Noncommercial 4.0 International License (CC-by the license) ( https://creativecommons.org/licenses/by-nc/4.0/ )
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Abstract

Pan, X.P., Zhang, G.Z., Liu, JX. and Ren, Z.Y., 2020. Estimating fluid term and anisotropic parameters in saturated transversely isotropic media with aligned fractures. Journal of Seismic Exploration, 30: 65-84. The Gassmann’s equation and general linear-slip model can be combined to characterize the effective elastic properties of a fluid-saturated transversely isotropic medium with aligned fractures. Such a medium represents a saturated fractured porous rock with orthorhombic symmetry. Combining the analysis of orthorhombic anisotropic poroelasticity, we first propose the derivation for the weak-anisotropy stiffnesses of a saturated fractured porous medium with orthorhombic symmetry in terms of the moduli of the background homogeneous isotropic rock, Thomsen-type anisotropy parameters, fracture weaknesses, and fluid modulus. Compared with the exact stiffness components, the approximated components of saturated fractured porous media with orthorhombic symmetry satisfy the actual demands in practical use. Using the approximately linearized expressions of the stiffness components of saturated orthorhombic model with the assumption of small Thomsen-type anisotropic parameters and small fracture parameters, we then derive a linearized PP-wave reflection coefficient in such an orthorhombic model, including a fluid term, a rigidity term, a density term, two Thomsen-type anisotropy terms, and three fracture-weakness terms. With a novel parameterization for Thomsen-type anisotropy parameters and fracture weaknesses, we derive an azimuthal elastic impedance equation with decoupled fluid term and anisotropic parameters. Synthetic and real data sets are used to illustrate the proposed approach in fluid saturated fractured porous rocks with orthorhombic symmetry, Sichuan Basin, China.

Keywords
orthorhombic symmetry
fracture weakness
Bayesian seismic inversion
saturated fractured porous media
decoupled fluid and fracture properties
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Journal of Seismic Exploration, Electronic ISSN: 0963-0651 Print ISSN: 0963-0651, Published by AccScience Publishing
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