基于声波测试法对鹰滩页岩各向异性分析

页岩储层通常呈薄层状结构，一般认为其岩石力学参数具有横向各向同性，而其各向异性受围压（CP）、含水率和总有机质含量（TOC）等多种因素的影响。本文对不同围压下的鹰滩（Eagle Ford）页岩进行超声波波速进行测试实验，研究围压对鹰滩页岩波速及岩石力学各向异性的影响。实验结果表明，鹰滩页岩属于弱各向异性多孔介质，并具有横向各向同性、垂向各向异性的性质。纵波（P波）和横波（S波）波速随围压的增大而增大，特别是在低围压范围内增幅显著，同时围压增大会降低纵波和横波的各向异性，纵波各向异性比横波各向异性对围压更敏感。对鹰滩页岩各向异性分析为页岩储层压裂过程中裂缝的起裂和延伸规律研究提供了必要的力学参数。

Anisotropic properties of the Eagle Ford shale by ultrasonic velocity measurements

Organic-rich gas shales are often composed of thin laminated structures which may be considered as transversely isotropic material. The anisotropic properties of shales are affected by many factors, including confining pressure, water content, and total organic content (TOC). This work performed ultrasonic velocity measurements at various confining pressures to investigate the effects of confining pressure on anisotropic properties of the Eagle Ford shale. Results show that the Eagle Ford shale is weak elastic anisotropic porous medium which has transversely isotropic and vertical anisotropic properties. Both compressional (P) and shear (S) wave velocities increase as confining pressure increase, especially at low confining pressure range. Increasing confining pressure decreases both P- and S-wave anisotropy and P-wave anisotropy is more sensitive to confining pressure than S-wave anisotropy. The analysis of anisotropic properties of Eagle Ford shale could provide useful mechanical parameters for understanding the initiation and distribution of fractures during hydraulic fracturing.