Absorption of strain waves in porous media at seismic frequencies |
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| Authors: | T L Chelidze H A Spetzler G A Sobolev |
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| Institution: | (1) Institute of Geophysics, Georgian Academy of Sciences, 1 Rukhadze str., 380093 Tbilisi, Georgia;(2) Bavarian Geoinstitute, Univ. Bayreuth, 95440 Bayreuth, Germany;(3) Present address: Dept. of Geological Sciences and CIRES, Univ. of Colorado, Box 216, 80309 Boulder, CO;(4) Institute of the Physics of the Earth, Russian Academy of Sciences, 10 Bolshaia Gruzinskaia, Moscow, Russia |
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| Abstract: | An understanding of strain wave propagation in fluid containing porous rocks is important in reservoir geophysics and in the monitoring in underground water in the vicinity of nuclear and toxic waste sites, earthquake prediction, etc. Both experimental and theoretical research are far from providing a complete explanation of dissipation mechanisms, especially the observation of an unexpectedly strong dependence of attenuationQ
–1 on the chemistry of the solid and liquid phase involved. Traditional theories of proelasticity do not take these effects into account. In this paper the bulk of existing experimental data and theoretical models is reviewed briefly in order to elecidate the effect of environmental factors on the attenuation of seismic waves. Low fluid concentrations are emphasized. Thermodynamical analysis shows that changes in surface energy caused by weak mechanical disturbances can explain observed values of attenuation in real rocks. Experimental dissipation isotherms are interpreted in terms of monolayered surface adsorption of liquid films as described by Langmuir's equation.In order to describe surface dissipation in consolidated rocks, a surface tension term is added to the pore pressure term in the O'Connell-Budiansky proelastic equation for effective moduli of porous and fractured rocks. Theoretical calculations by this modified model, using reasonable values for elastic parameters, surface energy, crack density and their geometry, lead to results which qualitatively agree with experimental data obtained at low fluid contents. |
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| Keywords: | Dissipation strain waves poroelasticity surface energy |
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