Stochastic characterization of discrete fractures in rock by hydraulic and tracer tomography

裂隙岩蕴藏着丰富的含水层，它们是增强型地热系统(EGS)的目标。这些研究对象共同面临的一个主要挑战是，如何恰当地描述与流动和运输过程相关的构造特征或裂缝系统。表征越准确，用数值模型模拟的过程就越可靠。数值模拟技术的最新发展令人印象深刻，在计算效率、真实感、高分辨率和耦合模拟方面的能力不断增强。尽管如此，数值模型相关的数据饥渴几乎没有可用的现场测量来满足。特别是每个场地独有的特征，如裂缝几何形状，需要协调的场地调查技术。即使对场地进行了很好的调查，也需要将测量数据整合到模型中的方法。该项目建议使用水和示踪剂注入的层析钻孔测试来识别和表征与流动和运输相关的裂缝。结合多口井的井间多水平测试成果，便于裂缝几何形状的重建。一个主要的新元素是通过一种通用的贝叶斯方法对记录的断层扫描信号进行反演，该方法迭代地调整裂缝方向、长度和裂缝密度(反向模型)。这与离散裂缝网络(正演模型)的灵活、快速的数值实施和模拟相结合。在有希望的初步结果的激励下，本文进一步发展了层析离散裂缝反演方法，以稳健地估计二维和三维系统中的裂缝概率。它是利用虚拟钻孔测试的合成数据以及裂隙岩石的现场实验中的压力和热示踪数据来阐述和演示的。

Fractured rocks host productive aquifers and they are the target for enhanced geothermal systems (EGS). A major challenge shared by these subjects is the appropriate characterization of structural features or fracture systems that are relevant for flow and transport processes. The more accurate the characterization, the more reliable the processes can be simulated by numerical models. Recent developments in numerical modelling techniques are impressive, with growing capabilities in computationally efficient, realistic, high-resolution and coupled simulation. Still, the associated data hunger of numerical models is barely fed by available field measurements. Especially features unique for each site, such as fracture geometries, require attuned site investigation techniques. And even if a site is well investigated, methods are needed for integrating measured data in a model. This project proposes the use of tomographic borehole tests with water and tracer injection to identify and characterize fractures relevant for flow and transport. By combining the insight from cross well multi-level tests in several boreholes, the reconstruction of fracture geometries is facilitated. A major novel element is the inversion of recorded tomographic signals by a versatile Bayesian approach that adjusts iteratively fracture orientations, lengths and fracture density (inverse model). This is combined with a flexible and fast numerical implementation and simulation of the discrete fracture network (forward model). Motivated by promising preliminary results, the proposed tomographic discrete fracture inversion approach is here further developed for robust estimation of fracture probabilities in two- (2D) and three-dimensional (3D) systems. It is elaborated and demonstrated utilizing synthetic data from virtual borehole tests, as well as by means of pressure and heat tracer data from in-situ experiments in fractured rock.