Mapping impedance microstructures in rocks with acoustic microscopy
Mapping impedance microstructures in rocks with acoustic microscopy
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DOI：
10.1190/1.1438902
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发表时间：
2001-02
期刊：
影响因子：
3.3
通讯作者：
M. Prasad
中科院分区：
文献类型：
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作者：
M. Prasad
各种方法可以表征储层岩石的微观结构特征，最终目的是将微观结构与地震性质联系起来。扫描电子显微镜、透射电子显微镜和光学显微镜传统上用于这类研究。他们认为岩性、孔隙空间、孔隙连通性、粒度和胶结是控制地震波速度和衰减的最重要因素。然而，这些技术只提供定性描述。这里介绍的声学技术，扫描声学显微镜（SAM）和声学探测（AS），可以映射，更重要的是，量化微观结构作为声阻抗的变化。超声应力波对弹性性质的局部变化很敏感，因此特别适合于表征储层岩石的微观结构性质。利用晶粒内部和样品界面之间的阻抗边界反射来构建微结构图像。声学显微技术是研究储层岩石内部结构和孔隙结构的有力工具。声学显微镜的基本原理与反射地震学的基本原理几乎相同。基于反射声波，即基于样品的阻抗变化，制备表面和亚表面微结构图像。样品上的声波进行模式转换，部分透射到样品中，部分反射。反射系数和换能器接收到的信号强度由材料的弹性常数决定。通过映射反射波，可以研究样品中声阻抗的变化对波反射特性的影响。由于声波的工作频率可以改变，因此可以控制声波在样品中的穿透深度和微观结构特征的分辨率。我将介绍高频SAM （0.1-2 GHz）和低频AS （25-100 MHz）的结果。在1ghz时，SAM的分辨率约为1 μm；为…
Various methods can characterize microstructural properties of reservoir rocks with the ultimate goal of relating microstructure to seismic properties. Scanning electron microscopy, transmission electron microscopy, and optical microscopy have traditionally been used for such studies. They have identified lithology, pore space, interconnectivity of pores, grain size, and cementation as the most important factors controlling seismic wave velocity and attenuation. However, these techniques provide qualitative descriptions only. The acoustic techniques presented here, scanning acoustic microscopy (SAM) and acoustic sounding (AS), can map and, more importantly, quantify microstructure as variations in acoustic impedance. Ultrasonic stress waves are sensitive to local variations in elastic properties and are therefore particularly suited for characterizing microstructural properties of reservoir rocks. Reflections from impedance boundaries in grains and between interfaces in the sample are used to construct the microstructural image. This paper will show that acoustic microscopy can be a powerful tool for studying internal structure and pore geometry of reservoir rocks. Acoustic microscopy's basic principle is almost identical to that of reflection seismology. Images of surface and subsurface microstructures are prepared on the basis of reflected acoustic waves—that is, on the impedance changes in the sample. Acoustic waves on a sample are mode converted, partly transmitted into the sample, and partly reflected. The reflection coefficient and with it the signal intensity received by the transducer are determined by the elastic constants of the material. Changes in acoustic impedance in the sample that influence wave reflection characteristics can be studied by mapping the reflected waves. Because the working frequency of the acoustic waves can be varied, their penetration depth into the sample and the resolution of microstructural features can be controlled. I will present results from high-frequency SAM (0.1–2 GHz) and low-frequency AS (25–100 MHz). The resolution of SAM is about 1 μm at 1 GHz; AS …