CAREER: Understanding transport processes in fractured sedimentary rock through multi-frequency and multi-method investigations

深层沉积岩是一种重要的、日益得到利用的资源，它提供了可开采地下水、石油和天然气的储集层，同样也提供了储存量。多余的水、废物或碳可以被隔离。然而，这些岩体中存在裂缝，这是大多数深部岩石的共同特征，这使得我们很难理解这些地层在开采或储存活动中的表现。沉积岩中的裂隙可以提供快速的流动路径，沿着这些路径可以发生集中流动和可能的沟道化流动。它们同样可以提供一个平面，流体可以沿着这个平面快速接触并与围岩发生反应。然而，使用现有的测试方法，我们了解突出裂缝平面内流动的能力是有限的。该项目的目的是：1)进一步开发了解裂缝流动过程的新测试方法；2)评估这些测试方法对裂缝的各种特征(例如，裂缝孔径变异性、裂缝硬度)的敏感性；以及3)在已知发生复杂裂缝流动的现场规模的研究现场，评估这些测试方法的真实性能。同样，该项目的一个更广泛的目标是更好地教育发展中的水文学家和广大公众，使他们了解岩石破裂的重要性及其对含水层流动和运输的影响。通过建立一个可见的骨折？在物理模型的基础上，我们将制作一个教育工具，使学生和其他人能够看到和评估污染物通过复杂断裂面的运动。这一教育工具以及其他地下水教育展品将通过巡回“弹出式”科学展览在全州范围内展示，该展览将把亲身实践的水文地质学带给周围的农村社区。沉积岩中的较厚空间通常提供了大部分水的存储空间，可能是流体流动的主要体积贡献者。然而，沉积岩中的裂隙使人们对这些物体中的流动和运输的理解变得非常复杂。裂缝可以使运移路径变得非常复杂，既有通过沉积物孔隙空间的扩散流动(即原生孔隙度)，也有集中的、可能是通过裂缝的沟道化流动(即次生孔隙度)，以及伴随而来的这两个域之间的流体交换。了解每一个过程的影响对于改进对这些含水层中污染物运移的预测至关重要，因为它们控制着通过含水层的溶质运移速度、溶质羽流的扩散以及溶质与围岩交换和化学反应的能力。振荡水力试验--在这种试验中，储集层内的流体压力以设定的频率正弦变化，并记录压力响应--已多次被认为是表征岩石裂缝的有用策略。然而，这种测试在实践中的应用显示了意想不到的反应，其中测试的岩石裂缝似乎具有“频率相关”的水力特性，这意味着裂隙平面内的复杂流动。引用Guiltinan和Becker(2015)的话说，这“表明表观水力参数的周期依赖性是地层中非均匀流动和储存的结果。因此，定期水力试验可能提供一种手段来表征基岩裂隙和裂隙网络中的流动通道。”这项提议将使用数值实验和现场规模的裂隙岩石测试来评估这一假设和其他与频率相关的假设。通过数值实验，该项目将评估多频振荡水力试验区分裂隙沉积岩中不同流动过程的能力。在现场范围内，将实施详细的振荡流动测试--单独和注气实验--以评估受控研究地点的流动通道和裂缝-宿主岩石交换的贡献。这项工作将首先评估裂隙平面内的非均质性程度和流动通道，使用已在实验室规模上显示出重大前景的振荡水力层析成像(OHT)成像。随后，将在注气后评估岩石裂缝对OHT测试的响应变化。这种多频率抽水试验方法是表征水流的一种强有力的工具，因为它将测量一系列时间尺度上的水文响应(以及水文过程)。

Deep sedimentary rocks represent an important and increasingly utilized resource, providing reservoirs from which groundwater, oil, and gas can be extracted, and similarly providing storage volumes in which ?banked? excess water, wastes, or carbon can be sequestered. However, the existence of fractures in these rock bodies, which are a common feature of most deep rocks, complicates our ability to understand how these formations will behave during either extraction or storage activities. Fractures in sedimentary rock can provide fast flow pathways along which focused and possibly channelized flow can occur. They can likewise provide a plane along which fluids can rapidly come into contact and react with surrounding rock. Our ability to understand flow within prominent fracture planes, however, is limited using existing testing methods. The purpose of this project is: 1) To further develop novel testing methods for understanding fracture flow processes; 2) To evaluate the sensitivity of these testing methods to various features of fractures (e.g., fracture aperture variability, fracture stiffness); and 3) To evaluate the real-world performance of these testing methods at a field-scale research site where complex fracture flow is known to occur. A broader goal of this project, similarly, is to better educate both developing hydrologists and the public at large about the importance of rock fractures and their impact on aquifer flow and transport. By building a ?visible fracture? physical model, we will produce an educational tool that allows students and others to see and assess the movement of contaminants through complex fracture planes. This educational tool, along with other groundwater educational exhibits, will be displayed across the state through a touring "pop-up" science exhibit that brings hands-on hydrogeology to the surrounding rural community.Pore spaces within sedimentary rock often provide the majority of storage space for water and may be the primary contributor by volume to fluid flow. However, fractures in sedimentary rock drastically complicate the understanding of flow and transport in these bodies. Fractures can make transport pathways quite complex, with a combination of diffuse flow through the sediment pore spaces (i.e., primary porosity), focused and possibly channelized flow through fractures (i.e. secondary porosity), and a concomitant exchange of fluids between these two domains. Understanding the impact of each of these processes is crucial for improving predictions of contaminant transport in these aquifers, as they control the rates of solute movement through the aquifer, the spreading of solute plumes, and the ability of solutes to exchange and react chemically with the host rock. Oscillatory hydraulic testing--in which fluid pressure within a reservoir is varied sinusoidally at a set frequency and pressure responses are recorded--has been suggested repeatedly as a useful strategy for characterizing rock fractures. Application of this testing in practice, however, has shown unexpected responses, in which a tested rock fracture appears to have "frequency dependent" hydraulic properties, implying complex flow within the fracture plane. To quote Guiltinan and Becker (2015) this "suggests that the period-dependency of apparent hydraulic parameters is a result of heterogeneous flow and storage in the formation. Thus, periodic hydraulic testing may provide a means to characterizing flow channeling in bedrock fractures and fracture networks." This proposal will assess this and other hypotheses for frequency dependence using numerical experiments and field-scale fractured rock testing. Through numerical experiments, the project will assess the ability of multi-frequency oscillatory hydraulic testing to distinguish between different flow processes in fractured sedimentary rock. At the field scale, detailed oscillatory flow testing will be implemented--alone and alongside gas injection experiments--to assess the contributions of flow channeling and fracture-host rock exchange at a controlled research site. Using oscillatory hydraulic tomography (OHT) imaging, which has shown significant promise at the laboratory scale, this work will first assess the degree of heterogeneity and flow channeling within a fracture plane. Following this, changes in the response of the rock fracture to OHT testing will be assessed after gas injection. This multi-frequency pumping test approach represents a powerful tool for characterizing flow in that it will measure hydrologic response (and thus, hydrologic processes) over a range of timescales.