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在围压为60MPa,频率约0.85NHz条件下,对29件水饱和砂岩及页岩试样,我们测量了其纵波及横波的速度及衰减情况。测量时,使用脉冲反射波法,将试样(直径为5cm,长1.5～2.5cm)置于高压容器内有机玻璃缓冲棒间。每一地震波的速度是根据从每一试样顶部和底部反射的信号等相点(作绕射效应校正)的传播时间差来确定。衰减数据以“品质因素”表示:Qp及Qs分别为纵波及横波的品质因素。结果表明,Qs对Vs强相关,而Qp对Vp弱相关,Qp对Qs强相关,Qp与孔隙内矿物组成的容积百分数强相关,不管矿物质是粘土或碳酸盐。结论是,衰减机理是由于基岩格架与孔隙内矿物组成的弹性模数相差很大,膨胀不均匀引起的局部流体流动所造成。
Under confining pressure of 60MPa and frequency of about 0.85NHz, we measured the velocity and attenuation of longitudinal and transverse waves on 29 water-saturated sandstone and shale samples. Measurement, the use of pulse reflection wave method, the sample (diameter of 5cm, length 1.5 ~ 2.5cm) placed in a high pressure container between the plexiglass buffer rod. The velocity of each seismic wave is determined on the basis of the propagation time differences of phase points (corrected for diffraction effects) of signals reflected from the top and bottom of each sample. The attenuation data is expressed as “quality factor”: Qp and Qs are the longitudinal and transverse wave quality factors, respectively. The results show that Qs strongly correlates with Vs, while Qp is weakly correlated with Vp, Qp strongly correlates with Qs, and Qp is strongly correlated with the volume fraction of mineral components in the pores, regardless of whether the minerals are clays or carbonates. The conclusion is that the attenuation mechanism is due to the large difference between the modulus of elasticity of the bedrock and the minerals in the pores, and the local fluid flow caused by the uneven expansion.