3D Imaging and Characterization of Fractures in Rock

岩石裂缝的 3D 成像和表征

• 批准号: 1536110
• 负责人: Bojan Guzina
• 金额: $ 34.57万
• 依托单位: University of Minnesota-Twin Cities
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2015
• 资助国家: 美国
• 起止时间: 2015-09-01 至 2019-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1536110&HistoricalAwards=false
• 关键词: 3D; Imaging; Characterization; Fractures; Rock

Geometric and interfacial properties of the fractures and faults in rock are the subject of critical importance to many facets of our society including mining, seismology, earthquake engineering, environmental protection, hydrogeology, and utilization of geothermal energy. One particular parameter embodying the fracture's interfacial condition is the so-called specific stiffness, quantifying for instance its rigidity under shearing or compression. Beyond its immediate relevance to the stability analyses in rock masses (e.g. during mining operations), the fracture specific stiffness has been found to: i) bear an intimate connection to the fracture's hydraulic properties (governing for example the performance of enhanced geothermal systems), ii) serve as a precursor of shear failure along rock discontinuities, and iii) help understand the mechanism of shallow earthquakes. In general, however, the fracture's response to given activation is equally driven by its geometry, which is inherently not limited to the planar condition. Thus a holistic characterization of subterranean fractures, that unveils both their geometric and mechanical characteristics, is a paramount. To help meet the challenge, this research aims to establish a comprehensive analytical, computational, and experimental platform for the geometric reconstruction and mechanical characterization of arbitrarily-shaped discontinuities in rock by way of seismic waves. The focus is on developing and validating a robust framework for the waveform tomography of fractures that is capable of resolving their three-dimensional geometry and spatial distribution of specific stiffness without iterations. Typically, approaches to the waveform tomography entail recursions owing to a highly nonlinear relationship between the fracture characteristics and seismic observations. Recently, however, the research in applied mathematics has produced a suite of non-iterative approaches to the waveform tomography such as the method of Topological Sensitivity. By building on such advancements, this research will cater for the imaging and characterization of curved fractures while allowing for significant flexibility in terms of the sensing arrangement. This is made possible by an innovative 3-step approach where the seismic waveforms are used to sequentially - and non-iteratively - reconstruct: i) fracture geometry, ii) fracture opening displacement profile, and iii) heterogeneous specific stiffness. The developments will be verified in a laboratory setting, making use of the recently acquired Scanning Laser Doppler Vibrometer that is capable of remotely monitoring triaxial waveforms on the surface of rock specimens with exceptional resolution and accuracy.

岩石裂缝和断层的几何和界面特性对于我们社会的许多方面都至关重要，包括采矿、地震学、地震工程、环境保护、水文地质学和地热能利用。体现裂缝界面条件的一个特定参数是所谓的比刚度，例如量化其在剪切或压缩下的刚度。 除了与岩体稳定性分析（例如采矿作业期间）直接相关之外，裂缝比刚度还被发现：i）与裂缝的水力特性密切相关（例如控制增强型地热系统的性能），ii）作为沿岩石不连续性剪切破坏的前兆，以及 iii）有助于了解浅层地震的机制。 然而，一般来说，裂缝对给定激活的响应同样由其几何形状驱动，其本质上不限于平面条件。 因此，对地下裂缝进行整体表征，揭示其几何和力学特征，是至关重要的。为了应对这一挑战，本研究旨在建立一个综合的分析、计算和实验平台，通过地震波对岩石中任意形状的不连续性进行几何重建和力学表征。 重点是开发和验证骨折波形断层扫描的稳健框架，该框架能够解析其三维几何形状和比刚度的空间分布，而无需迭代。 通常，由于裂缝特征和地震观测之间的高度非线性关系，波形层析成像方法需要递归。 然而，最近应用数学的研究产生了一套波形断层扫描的非迭代方法，例如拓扑灵敏度方法。 通过在这些进步的基础上，这项研究将满足弯曲裂缝的成像和表征，同时在传感布置方面实现显着的灵活性。 这是通过创新的三步方法实现的，其中地震波形用于顺序且非迭代地重建：i) 裂缝几何形状，ii) 裂缝张开位移剖面，以及 iii) 异质比刚度。这些进展将在实验室环境中得到验证，利用最近购买的扫描激光多普勒测振仪，该测振仪能够以卓越的分辨率和精度远程监测岩石样本表面的三轴波形。