摘要
选择具有不同孔隙度的三种岩石样品,在最高达600MPa (干燥样品)或300MPa (水饱和样品)的不同围压条件下,同时测量了在其中传播的纵、横波的速度及衰减。对于低孔隙度的花岗岩,干燥和水饱和样品的 Q 值几乎没有差别,但与干燥样品相比,水饱和样品中的纵波速度较高而横波速度稍低。对于中等孔隙度的杂砂岩,干燥样品和水饱和样品的波速和 Q 值及其随围压的变化有明显的不同。在高孔隙度的砂岩中这种不同更加显著。综合分析同时测得的纵、横波速度和 Q 值可以发现,当围压增加时,低孔隙度的花岗岩中同体应变相关的能量损失与同剪切应变相关的能量损失之比减小,但在中等孔隙度的杂砂岩和高孔隙度的砂岩中这一比值增大;同时,水饱和样品中的这一比值要比干燥样品中的大,而且它们之间的差别同样品的孔隙度正相关。
Q-values for P-and S-waves along with the respective velocities have been determined for a low-porosity granite (0.7%) from Petras (Portugal),a mid-porosity graywacke (9%) and a high-porosity sandstone (21%) from Xinjiang under confining pressures up to 600MPa (for dry samples) or 300MPa (for wet samples).The simultaneous measurements of velocities and Q provide information on the mechanisms of attenuation,especially for an assessment of whether the predominant damping mechanism is in shear or in compression.Through analysis,we may find that,as confining pressure increases the ratio between damping related to compressive strain and which related to shear strain decreases in the low-porosity granite but increases in the mid-porosity gmywacke and the high-porosity sandstone,also this ratio is bigger in wet sample than in dry sample and the difference between them is proportional to the sample's porosity.At high confining pressures the velocities are determined by the mineral composition and the single crystal properties of the major constituents.In contrast,the Q-values are mainly controlled by grain boundary effects.
出处
《地球物理学报》
SCIE
EI
CAS
CSCD
北大核心
1998年第4期537-546,共10页
Chinese Journal of Geophysics
基金
中国科学技术大学青年基金
关键词
超声波速
围压
水饱和
孔隙度
岩样
纵横波速度
Ultrasonic velocities
Attenuation
Confining pressure
Water saturation
Porosity.
