饱和砂岩的黏弹行为的实验研究

Experimental research on viscoelastic behavior for saturated rocks

通过Metravib热机械分析仪,用正弦波进行加载,实验时固定静载为100N,正弦波动载荷恒为60 N,将总载荷控制在屈服点以下;在温度为—50～125℃,升温速率为1℃/min,频率为5～1000 Hz的条件下,对泵油饱和长石砂岩、彭山砂岩样品进行单轴循环加载实验,求取泵油饱和长石砂岩和彭山砂岩的衰减、耗散角、模量、波速与温度和频率的关系.以此研究了饱和多孔岩石在弹性范围内的衰减、耗散角、杨氏模量和弹性波波速随温度和频率的变化规律.取得了随频率或温度增高饱和多孔岩石的衰减峰和耗散角峰的峰位向高温或高频方向移动的热激活弛豫规律.以低频共振衰减解释了随频率增高衰减强度增大;用阻尼衰减和以岩石天然孔隙裂缝随疲劳载荷时间的增长,裂缝纵横比增加,解释了随频率增高,衰减峰的峰位向高频方向移动和衰减峰的强度降低的另一实验结果.这些实验结果与低频共振的驻波实验取得了同样的热激活弛豫规律,说明热激活弛豫机制在饱和多孔岩石中具有一定的普适性.本文还获得了杨氏模量和弹性波波速随温度升高而下降,随频率增高而增大,具有频散效应,随温度升高频散效应有减弱的趋势.该研究结果对理论模型研究具有指导意义,对地震资料的解释具有实用意义.

Experiments are performed by Metravib Dynamic Mechanical Analyzer （DMA＋450） under sine wave loading to simulate the seismic wave. The static load is fixed to 100N, and the dynamic load of the sine wave is 60N so that the total loading force is controlled under yield stress. Temperature is controlled between -50℃ and 125℃, and the heating speed is I℃ per minute. The frequency range is from 5 Hz to 1000 Hz. Pump-oil saturated arkoses and Pengshan sandstones are tested under uniaxial cyclic loading. The variations of attenuation, phase angle,modulus, and velocity with temperature or frequency are obtained. The attenuation peak and the phase angle peak shift to higher temperatures or higher frequencies when the frequency or temperature increases, which can be considered as thermal relaxation regularities. The increasing of attenuation with frequency can be explained by low-frequency resonance. The move of the attenuation peak and increasing of attenuation with frequency can be explained by damping. The aspect ratio of the micro cracks in rock samples would increase with the fatigue loading. The variation of aspect ratio can explain the phenomenon that the attenuation peak value decreases when the frequency increases and the peak shifts to higher frequencies. The experimental results and phenomena are similar to the low-frequency resonance standing wave experiments. Thus the thermal relaxation regularities generally exist for saturated porous rocks. The Youngrs modulus and velocity increase with frequency and decrease when temperature increases. There is obvious frequency dispersion, and the dispersion weakens when temperature increases. This investigation is very helpful to study of theoretical model and seismic data interpretation.