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Type: Artigo de periódico
Title: Uniaxial Stress And Ultrasonic Anisotropy In A Layered Orthorhombic Medium
Author: Omoboya B.
De Figueiredo J.J.S.
Dyaur N.
Stewart R.R.
Abstract: Studies of orthorhombic anisotropy are becoming progressively essential, especially as many sedimentary rocks are considered to have orthorhombic symmetry. To study the effect of stress in a layered orthorhombic medium, a physical modeling study using intrinsically orthorhombic phenolic boards was conducted. The experiment was designed to simulate sedimentary reservoir rocks deposited in layers with inherent orthotropic symmetry and under the influence of stress due to overlying sediments. The study also explores which geologic phenomena dominate the contortion of anisotropy under different stress tenure. The phenolic boards were coupled together with the help of a pressure device and uniaxial stress was gradually increased while time arrival and velocity measurements were repeated. Results show maximum increase in compressional and shear wave velocities ranging from 4% to 10% in different directions as a function of increasing uniaxial stress. P and S wave dependent stiffness coefficients generally increased with stress. Anisotropic parameters {left parenthesis, less than bracket}extension of Thomsen's parameters for orthorhombic symmetry{right parenthesis, greater than bracket} generally diminished or remained constant with increasing pressure and changes ranged from 0% to 33%. We observed anisotropic behavior a priori to both orthorhombic and VTI symmetries in different principal axes of the model. Polar anisotropy behavior is due primarily to layering or stratification and tends to increase with pressure. Certain anisotropic parameters however unveil inherent orthotropic symmetry of the composite model. © 2011 Society of Exploration Geophysicists.
Rights: fechado
Identifier DOI: 10.1190/1.3627634
Date Issue: 2011
Appears in Collections:Unicamp - Artigos e Outros Documentos

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