| 英文摘要: | 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. |