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Characterization and modeling of the stress and pore-fluid dependent acoustic properties of fractured porous rocks.

机译：裂隙多孔岩石应力和孔隙流体相关的声学特性的表征和建模。

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摘要

The thesis presents the results of a study of the characterization and modeling of the stress and pore-fluid dependent acoustic properties of fractured porous rocks. A new laboratory High Pressure and High Temperature (HPHT) triaxial testing system was developed to characterize the seismic properties of sandstone under different levels of effective stress confinement and changes in pore-fluid composition. An intact and fractured of Berea sandstones core samples were used in the experimental studies. The laboratory test results were used to develop analytical models for stress-level and pore-fluid dependent seismic velocity of sandstones.;Models for stress-dependent P and S-wave seismic velocities of sandstone were then developed based on the assumption that stress-dependencies come from the nonlinear elastic response of micro-fractures contained in the sample under normal and shear loading. The contact shear stiffness was assumed to increase linearly with the normal stress across a micro-fracture, while the contact normal stiffness was assumed to vary as a power law with the micro-fracture normal stress. Both nonlinear fracture normal and shear contact models were validated by experimental data available in the literature.;To test the dependency of seismic velocity of sandstone on changes in pore-fluid composition, another series of tests were conducted where P and S-wave velocities were monitored during injection of supercritical CO 2 in samples of Berea sandstone initially saturated with saline water and under constant confining stress. Changes in seismic wave velocity were measured at different levels of supercritical CO2 saturation as the initial saline water as pore-fluid was displaced by supercritical CO 2. It was found that the P- iv wave velocity significantly decreased while the S-wave velocity remained almost constant as the sample supercritical CO2 saturation increased. The dependency of the seismic velocity on changes on pore fluid composition during injection of supercritical CO 2 in Berea sandstone was modeled using a re-derived Biot-Gassmann substitution theory. In using the Biot-Gassmann substitution theory, it was found necessary to account for the changes in the pore-fluid compressibility in terms of the volumetric proportion and distribution of saline water and supercritical CO 2 in the sample pore space. This was done by using the empirical model of Brie et al. to account for the compressibility of mixtures of two-phase immiscible fluids. The combined Biot-Gassman and Brie et al. models were found to represent adequately the changes in P-wave velocity of Berea sandstone during displacement of saline water by supercritical CO2.;The third experimental and modeling study addressed shear-wave splitting due to the presence of fractures in a rock mass. Tests were conducted using the high temperature and high pressure (HPHT) triaxial device on samples of Berea sandstone, containing a single induced tensile fracture running along the height of the sample. The fracture was created via a modified Brazilian Split Test loading where the edges of cylindrical samples were loaded on diametrically opposite two points by sharp guillotines. The Joint Roughness Coefficient (JRC) values of the fractured core samples were determined by profilometry and tilt test. The effect of mismatching of the fracture surfaces on shear wave splitting was investigated by applying different amounts of shear displacements to three core samples. The degree of mismatching of the fracture surfaces in the core samples was evaluated using the Joint Matching Coefficient (JMC). Shear-wave splitting, as measured by the difference in magnitudes of shear-wave velocities parallel and perpendicular to the fracture, Vs1 and Vs2 respectively, increases with increasing mismatch of the fracture surfaces and decreases with increasing effective stress, and approaches zero in the effective stress range tested. A model for the stress and JMC dependent shear-wave splitting was developed based on the experimental observations.;Finally, the magnitude of shear-wave splitting was correlated with the permeability of the fractured porous sandstone for fluid flow parallel to the induced fracture. (Abstract shortened by UMI.).
机译：本文介绍了裂隙多孔岩石应力和孔隙流体相关的声学特性的表征和建模的研究结果。开发了一种新的实验室高压高温（HPHT）三轴测试系统，以表征在不同有效应力限制和孔隙流体组成变化条件下砂岩的地震特性。在实验研究中使用了完整且破裂的Berea砂岩岩心样品。实验室测试结果用于建立砂岩应力水平和孔隙流体相关地震速度的分析模型;在假设应力依赖性的前提下，开发了砂岩应力相关的P波和S波地震速度模型来自正常和剪切载荷下样品中微裂纹的非线性弹性响应。假定接触剪切刚度随微裂缝的法向应力线性增加，而假定接触正交刚度随微裂缝法向应力的幂律变化。非线性裂缝法线和剪切接触模型都通过文献中的实验数据进行了验证。为了测试砂岩的地震速度对孔隙流体组成变化的依赖性，还进行了一系列的P和S波速度测试。在最初用盐水饱和并处于恒定围压下的Berea砂岩样品中注入超临界CO 2期间进行监测。在超临界CO2饱和度不同水平下测量了地震波速度的变化，因为最初的盐水通过超临界CO 2置换了孔隙流体。发现P-iv波速显着下降，而S波速几乎保持不变当样品超临界CO2饱和度增加时保持恒定。利用重新推导的Biot-Gassmann替代理论，模拟了Berea砂岩中超临界CO 2注入过程中地震速度对孔隙流体组成变化的依赖性。在使用Biot-Gassmann替代理论时，发现有必要根据样品孔隙空间中盐水和超临界CO 2的体积比例和分布来考虑孔隙流体可压缩性的变化。这是通过使用Brie等人的经验模型完成的。考虑到两相不混溶流体混合物的可压缩性。 Biot-Gassman和Brie等人的结合。该模型被发现可以充分代表Berea砂岩在超临界CO2驱替盐水过程中P波速度的变化。第三次实验和建模研究解决了由于岩体中存在裂缝而引起的剪切波分裂。使用高温高压（HPHT）三轴设备对Berea砂岩样品进行了测试，该样品包含沿样品高度延伸的单个诱发拉伸断裂。骨折是通过修改后的巴西劈裂试验载荷产生的，其中圆柱形样品的边缘由锋利的断头台沿直径相对的两个点加载。通过轮廓测定法和倾斜试验确定断裂的芯样品的接头粗糙度系数（JRC）值。通过对三个岩心样品施加不同量的剪切位移，研究了断裂面失配对剪切波分裂的影响。使用联合匹配系数（JMC）评估岩心样品中断裂表面的失配程度。剪切波分裂是通过平行于和垂直于裂缝的剪切波速度大小的差异来衡量的，Vs1和Vs2分别随着裂缝表面失配的增加而增加，并随着有效应力的增加而减小，并且在有效裂缝中接近零。测试压力范围。在实验结果的基础上，建立了应力与JMC相关的剪切波分裂模型。最后，剪切波分裂的大小与裂缝性多孔砂岩的渗透率平行，与渗透率相关。 （摘要由UMI缩短。）。

著录项

  • 作者

    Almrabat, Abdulhadi M.;

  • 作者单位

    Colorado School of Mines.;

  • 授予单位 Colorado School of Mines.;
  • 学科 Civil engineering.;Geophysical engineering.
  • 学位 Ph.D.
  • 年度 2013
  • 页码 148 p.
  • 总页数 148
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类
  • 关键词

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