岩石动态与静态弹性参数差别的微观机理

MICROSCOPIC MECHANISM OF DIFFERENCE BETWEEN STATIC AND DYNAMIC ELASTIC PARAMETERS OF ROCK

根据对岩石动、静态弹性参数的观测结果及岩石力学与岩石物理学的相关理论 ,对动、静态弹性参数差别的微观机理进行了分析。结果表明 ,动、静态弹性参数存在差别是由于岩石内部存在微裂隙与孔隙流体。在不同应变幅值和频率的动、静态载荷作用下 ,微裂隙与孔隙流体的微观变形特征不同。在静态大应变下 ,沿颗粒边界或裂隙面的摩擦滑动使岩石表观模量减小 ,而声波引起的应变很小 ,不足以引起这种滑动。另外 ,动态载荷下岩石处于“不排水”状态 ,并因“粒间喷流”引起模量频散 。

Based on the experimental results and rock mechanics and rock physics, the microscopic mechanism of difference between static and dynamic elastic parameters is analyzed. The inherent cause of this difference is the rock constituent and structure, such as fissure, soft pore and weak contact between rock grains, and existance of pore fluid in rock. The microscopic changes of microfracture and pore fluid are varied under different action of static and acoustic loadings with different strain amplitude and frequency. A load with a larger strain is exerted to the sample for static test while a cyclic load with a high frequency and a small strain for the dynamic test. Rocks response differently to static and dynamic loads. Static load with a larger strain causes the rock friction sliding across the crack faces or grain boundary, which makes the rock softened. Dynamic strain amplitude is too small to induce this friction sliding. Strain amplitude has no effect on dynamic moduli. Rocks undergo a 'undrained' compression during the propagation of elastic wave, which makes the rock stiffened. A squirt flow happening at higher frequency increases the rock dynamic moduli furthermore, i.e., moduli dispersion. All of these make the static and dynamic moduli different, and the dynamic modulus is higher. Moduli dispersion causes different correlations between static and dynamic elastic properties when the static properties from seismic and ultrasonic velocities are different.