孔洞结构对超声波衰减特性的影响研究

 碳酸盐岩地层孔洞形状多样、孔洞空间尺度多变、分布复杂，以首波触发机制记录的波速，反映的是沿着波阻抗最大路径传播的声波速度，不能有效反映岩石中的孔洞结构特征。基于波动理论和有限差分方法，实现超声波透射数值模拟实验，研究孔洞形状、尺寸、分布、密度对声波衰减系数的影响。结果表明：(1) 孔洞形状、尺寸、分布、密度对衰减系数均有影响，其中孔洞密度对衰减系数的影响最大，孔洞尺寸次之，孔洞形状和分布对衰减系数的影响较小；(2) 垂直于传播方向的孔洞尺寸和平行于传播方向上的孔洞尺寸均对衰减系数有影响，相对而言垂直于传播方向上孔洞尺寸对衰减系数的影响更显著；(3) 对一定频率的振源，存在一个临界孔洞尺寸，当孔洞的尺寸大于该临界值时，不能应用衰减系数反映孔隙尺寸的变化；(4) 衰减系数与孔洞尺寸、不同孔洞形状的孔隙度之间均表现为幂函数关系，且相关性较好。

STUDY OF EFFECT OF PORE STRUCTURE ON ULTRASONIC ATTENUATION

For the variety pore shape，the multi-scale pore space and the complex pore distribution in carbonate，The characteristics of the pore and hole structure can?t be obtained with the velocity of primary wave，which is the result along the path of the maximum wave impedance. Based on the wave theory and finite difference method，Numerical simulation of ultrasonic transmission has been achieved. And the relation between attenuation factor and the pore shape，size，distribution and density has been studied. According to the study，the conclusion is as follows：(1) Attenuation factor was significantly influence the pore shape，pore size，pore distribution and pore density. And the effect of pore density on the attenuation factor is the most significant. And the pore shape and distribution have less influence on attenuation factor. (2) Whether in the vertical direction or parallel to the propagation direction，pore size have significant influence on the attenuation. And the pore size which perpendicular to the direction of propagation have more influence. (3) For certain frequency vibration source，there is the critical pore size. If the pore size is bigger than the critical size，the changes of pore size cannot be analyzed by the attenuation coefficient. (4) The relationship between attenuation coefficient and pore size，porosity with different pore shapes was expressed as power function with better correlation.