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、日益被利用的资源，它提供了可以提取地下水、石油和天然气的储层，同样也提供了储藏库。多余的水、废物或碳可以被隔离。然而，这些岩体中存在裂缝，这是大多数深层岩石的共同特征，使我们理解这些岩层在开采或储存活动中的行为变得复杂。沉积岩中的裂缝可以提供快速的流动通道，沿着这些通道可以发生集中流动和可能的渠化流动。它们还可以提供一个平面，使流体沿着这个平面迅速接触并与周围的岩石发生反应。然而，利用现有的测试方法，我们了解突出裂缝面内流动的能力受到限制。该项目的目的是：1)进一步发展新的测试方法，以了解裂缝流动过程；2)评价这些检测方法对裂缝各种特征（如裂缝孔径变异性、裂缝刚度）的敏感性；3)在已知发生复杂裂缝流动的现场规模研究现场评估这些测试方法的实际性能。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，使他们了解岩石断裂的重要性及其对含水层流动和运输的影响。通过建立？可见骨折?物理模型，我们将制作一个教育工具，让学生和其他人看到并评估污染物通过复杂裂缝面的运动。这个教育工具，连同其他地下水教育展品，将通过巡回的“弹出式”科学展览在全州展出，为周围的农村社区带来亲身实践的水文地质学。沉积岩中的孔隙空间通常为水提供了大部分存储空间，并且可能是流体流动的主要贡献者。然而，沉积岩中的裂缝极大地复杂化了对这些体中流动和搬运的理解。裂缝可以使运移路径变得相当复杂，通过沉积物孔隙空间的弥漫性流动（即原生孔隙），通过裂缝的集中和可能的通道化流动（即次生孔隙），以及这两个区域之间伴随的流体交换。了解每一个过程的影响对于改善这些含水层中污染物运移的预测至关重要，因为它们控制着溶质在含水层中的移动速率、溶质柱的扩散以及溶质与宿主岩石交换和化学反应的能力。振荡水力测试是指储层内的流体压力在设定的频率下呈正弦变化，并记录压力响应。振荡水力测试已被多次建议作为表征岩石裂缝的有用策略。然而，在实际应用中，该测试显示出意想不到的反应，其中测试的岩石裂缝似乎具有“频率依赖”的水力特性，这意味着裂缝平面内的复杂流动。引用Guiltinan和Becker（2015）的话，这“表明表观水力参数的周期依赖性是地层中不均匀流动和储存的结果。因此，定期的水力测试可以为基岩裂缝和裂缝网络中的流动通道提供表征手段。”该提案将通过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频率依赖性假设。通过数值实验，本项目将评估多频振荡水力试验区分裂缝性沉积岩中不同流动过程的能力。在现场规模上，将实施详细的振荡流动测试（单独进行或与注气实验一起进行），以评估在受控研究地点的流动通道和裂缝-宿主岩石交换的贡献。振荡水力层析成像（OHT）在实验室规模上显示出了巨大的前景，这项工作将首先评估裂缝平面内的非均质性和流动通道的程度。在此之后，将在注气后评估岩石裂缝对高温测试的响应变化。这种多频泵送测试方法是表征流量的有力工具，因为它可以测量一定时间尺度内的水文响应（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.