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| STUDY OF VISCOELASTIC BEHAVIOR OF SATURATED ROCKS BY USING NON-FORCED RESONANCE METHOD |
| XI Daoying1，2，XU Songlin3，ZHOU Chengguang4，DU Yun1，2，XI Jun5 |
| (1. Mengcheng National Geophysical Observatory，University of Science and Technology of China，Hefei，Anhui 230026，China；2. School of Earth and Space Science，University of Science and Technology of China，Hefei，Anhui 230026，China；3. Key Laboratory for Mechanical Behavior and Design of Materials of Chinese Academy of Sciences，University of Science and Technology of China，Hefei，Anhui 230027，China；4. Key Laboratory of Noise and Vibration Research，Institute of Acoustics，Chinese Academy of Sciences，Beijing 100190，China；5. School of Mechanical Engineering，Beijing Institute of Petrochemical Technology，Beijing 102671，China) |
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Abstract Employing Metravib dynamic mechanical analyzer，saturated rock samples are loaded under sine wave loading model to simulate the viscoelastic behavior when seismic wave propagating in viscoelastic media. The static load is fixed to 120 N，and the dynamic load of the sine wave is 80 N；so that the total loading force is controlled under yield stress. Temperature is controlled between －40 ℃ and 100 ℃，and the frequency range is from 5 Hz to 400 Hz. Such two kinds of saturated rocks as pump-oil saturated Pengshan sandstones with two different porosities are tested under uniaxial cyclic loading. The variations of attenuation，elastic modulus，and elastic wave velocity with temperature or frequency are obtained. The energy attenuation peaks shift to higher temperatures when the frequency increases，which can be considered as thermal relaxation regularities. Damping attenuation mechanism is used to explain the experimental result that amplitude of attenuation peak decreases with the increasing frequency. The experimental results are in accord with the thermal relaxation regularities obtained by low-frequency resonant standing wave experiments，which show that the thermal relaxation regularities may widely exist in saturated rocks. The experimental results indicate that the elastic modulus and velocity increase with the increasing frequency and decrease when temperature increases. There is obvious frequency dispersion，and the dispersion weakens at high temperature area. The studies of ranges of frequency and temperature are very helpful to the study of theoretical model and seismic data interpretation. Study of attenuation of saturated rock is valuable for geophysical exploration，especially the exploration of geothermal steam or gas reservoirs.
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Received: 17 November 2011
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2012, Vol. 31 
