砂岩弹性参数与波速关系的实验研究

Experimental Study on Relations between Elastic Modulus and Wave Velocity of Sandstone

为进一步了解岩石弹性参数(如杨氏模量、泊松比)与超声波波速的关系,将岩石加卸载循环实验和超声波测量实验同时进行,得到同一组样品的测量数据并作对比分析。实验结果表明,应力的变化会导致岩石样品的孔隙度、裂隙、岩石结构和构造的改变。受这些因素的影响砂岩的杨氏模量、泊松比、波速,也都会有规律地变化。较低应力水平时用小循环加卸载测得的动态弹性模量是不准确的,计算的波速也不准确,只有通过波速实验才能准确测出;饱水情况的加卸载纵波波速之差比干燥情况小,饱水波速大于干燥波速;动态泊松比比较稳定,但静态泊松比随着应力的增加而增加,从0.07增加到0.12,有趋近于动态泊松比的趋势;用P-M模型从微观概率分布入手,能够很好地解释静态和动态弹性参数的差别。通过本实验,采用回归分析的方法,成功建立起了岩石介质中弹性参数与波速的关系,为类似实验提供参考依据。

To further understand the relationship between rock elastic parameters （ such as Young′s modulus, Poisson′s ratio） and the ultrasonic velocity, the rock loading and unloading cycle experiments and ultrasonic meas-urement experiments are carried out at the same time.The data of the same set of samples are obtained for compara-tive analysis, and the experimental results show that, the change of stress can cause changes in the porosity of the rock sample, fracture, and rock structure.The Young′s modulus, Poisson′s ratio and velocity of sandstone also change regularly with these factors above.The dynamic elastic modulus of low stress level with a small cyclic load-ing and unloading measurement is not accurate, so the calculation of the velocity is neither accurate, and the modu-lus can be only measured using the velocity experiments.The differential water saturated P-wave velocity of loading and unloading is smaller than that of dry conditions, but saturated P-wave velocity is greater than the dry velocity. The dynamic Poisson′s ratio is relatively stable, always in about 0.15;but the static Poisson′s ratio increased with the increase of stress, increased from 0.07 to 0.12, there is a trend close to dynamic Poisson′s ratio.P-M model from the microscopic probability distribution perspective gives a rational explanation of the difference between static and dynamic elastic parameters.Through the experiment, using the method of regression analysis, the relationship between the elastic parameters and wave velocity of rock medium is established and provides reference for later simi-lar experiments.