Characterizing Bedrock Fracture Flow Properties Through Multi-frequency Oscillatory Flow Interference Testing PDF Download
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Author: Jeremy R. Patterson
Publisher:
ISBN:
Category :
Languages : en
Pages : 0
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Book Description
Fractured sedimentary bedrock aquifers represent critical groundwater resources that provide significant domestic and agricultural water supplies as well as idealized targets for wastewater storage and alternative energy development. The complex flow pathways occurring within fractured bedrock has led to flow and transport phenomena that are critical to understand, yet difficult to predict, highlighting the necessity of moving beyond traditional porous media approaches to modeling bedrock fracture flow and transport. Characterizing the physical properties that govern fluid flow and storage in bedrock fractures represents a critical first step in developing the next generation of models that capture these complex hydraulic processes. Recent field and modeling studies highlight oscillatory flow interference testing as a novel pressure-based approach to characterize the hydraulic properties of bedrock fractures, and found that the returned effective hydraulic parameters show an apparent period-dependence when using simplified modeling approaches. In this dissertation, I use a combination of field and numerical modeling experiments to investigate a range of potential mechanisms - such as heterogeneity, fracture-host rock fluid exchange, and fracture hydromechanics - that might be contributing to this apparent period-dependence. Chapter 2 describes a novel gradient-based inversion strategy to determine effective aquifer flow properties and provides uncertainty estimates in returned parameters. This analysis shows that a multi-frequency inversion approach provides additional information that helps constrain the inversion and reduces parameter uncertainty estimates. Chapter 3 describes 209 oscillatory flow experiments conducted at a fractured sedimentary bedrock site near Madison, Wisconsin. Using simplified analytical modeling approaches, this analysis shows an apparent period-dependence in the collected field data, and indicates non-Darcian flow, borehole storage, and fracture leakance do not contribute to the apparent period dependence at our field site. Chapter 4 presents a comprehensive numerical modeling study that systematically explores fracture aperture heterogeneity, fracture-host rock fluid exchange, and fracture hydromechanical behavior to explain the apparent period-dependence. This analysis shows that fracture hydromechanical behavior is the only investigated mechanism that consistently reproduces the previously reported period-dependent parameter trends in direction and magnitudes of change, though other explored mechanisms produce period-dependent trends that could represent helpful diagnostic criteria of processes occurring at a specific site. Overall, the results of this dissertation highlight the need to develop more complex numerical modeling approaches that account for complex fracture hydraulics when characterizing fractured bedrock aquifer systems.
Author: Jeremy R. Patterson
Publisher:
ISBN:
Category :
Languages : en
Pages : 0
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Book Description
Fractured sedimentary bedrock aquifers represent critical groundwater resources that provide significant domestic and agricultural water supplies as well as idealized targets for wastewater storage and alternative energy development. The complex flow pathways occurring within fractured bedrock has led to flow and transport phenomena that are critical to understand, yet difficult to predict, highlighting the necessity of moving beyond traditional porous media approaches to modeling bedrock fracture flow and transport. Characterizing the physical properties that govern fluid flow and storage in bedrock fractures represents a critical first step in developing the next generation of models that capture these complex hydraulic processes. Recent field and modeling studies highlight oscillatory flow interference testing as a novel pressure-based approach to characterize the hydraulic properties of bedrock fractures, and found that the returned effective hydraulic parameters show an apparent period-dependence when using simplified modeling approaches. In this dissertation, I use a combination of field and numerical modeling experiments to investigate a range of potential mechanisms - such as heterogeneity, fracture-host rock fluid exchange, and fracture hydromechanics - that might be contributing to this apparent period-dependence. Chapter 2 describes a novel gradient-based inversion strategy to determine effective aquifer flow properties and provides uncertainty estimates in returned parameters. This analysis shows that a multi-frequency inversion approach provides additional information that helps constrain the inversion and reduces parameter uncertainty estimates. Chapter 3 describes 209 oscillatory flow experiments conducted at a fractured sedimentary bedrock site near Madison, Wisconsin. Using simplified analytical modeling approaches, this analysis shows an apparent period-dependence in the collected field data, and indicates non-Darcian flow, borehole storage, and fracture leakance do not contribute to the apparent period dependence at our field site. Chapter 4 presents a comprehensive numerical modeling study that systematically explores fracture aperture heterogeneity, fracture-host rock fluid exchange, and fracture hydromechanical behavior to explain the apparent period-dependence. This analysis shows that fracture hydromechanical behavior is the only investigated mechanism that consistently reproduces the previously reported period-dependent parameter trends in direction and magnitudes of change, though other explored mechanisms produce period-dependent trends that could represent helpful diagnostic criteria of processes occurring at a specific site. Overall, the results of this dissertation highlight the need to develop more complex numerical modeling approaches that account for complex fracture hydraulics when characterizing fractured bedrock aquifer systems.
Author: Frances Claire Sayler
Publisher:
ISBN:
Category :
Languages : en
Pages : 151
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Book Description
Author: Committee on Fracture Characterization and Fluid Flow
Publisher: National Academies Press
ISBN: 0309563488
Category : Science
Languages : en
Pages : 568
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Book Description
Scientific understanding of fluid flow in rock fractures--a process underlying contemporary earth science problems from the search for petroleum to the controversy over nuclear waste storage--has grown significantly in the past 20 years. This volume presents a comprehensive report on the state of the field, with an interdisciplinary viewpoint, case studies of fracture sites, illustrations, conclusions, and research recommendations. The book addresses these questions: How can fractures that are significant hydraulic conductors be identified, located, and characterized? How do flow and transport occur in fracture systems? How can changes in fracture systems be predicted and controlled? Among other topics, the committee provides a geomechanical understanding of fracture formation, reviews methods for detecting subsurface fractures, and looks at the use of hydraulic and tracer tests to investigate fluid flow. The volume examines the state of conceptual and mathematical modeling, and it provides a useful framework for understanding the complexity of fracture changes that occur during fluid pumping and other engineering practices. With a practical and multidisciplinary outlook, this volume will be welcomed by geologists, petroleum geologists, geoengineers, geophysicists, hydrologists, researchers, educators and students in these fields, and public officials involved in geological projects.
Author: National Academies of Sciences, Engineering, and Medicine
Publisher: National Academies Press
ISBN: 0309373727
Category : Science
Languages : en
Pages : 177
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Book Description
Fractured rock is the host or foundation for innumerable engineered structures related to energy, water, waste, and transportation. Characterizing, modeling, and monitoring fractured rock sites is critical to the functioning of those infrastructure, as well as to optimizing resource recovery and contaminant management. Characterization, Modeling, Monitoring, and Remediation of Fractured Rock examines the state of practice and state of art in the characterization of fractured rock and the chemical and biological processes related to subsurface contaminant fate and transport. This report examines new developments, knowledge, and approaches to engineering at fractured rock sites since the publication of the 1996 National Research Council report Rock Fractures and Fluid Flow: Contemporary Understanding and Fluid Flow. Fundamental understanding of the physical nature of fractured rock has changed little since 1996, but many new characterization tools have been developed, and there is now greater appreciation for the importance of chemical and biological processes that can occur in the fractured rock environment. The findings of Characterization, Modeling, Monitoring, and Remediation of Fractured Rock can be applied to all types of engineered infrastructure, but especially to engineered repositories for buried or stored waste and to fractured rock sites that have been contaminated as a result of past disposal or other practices. The recommendations of this report are intended to help the practitioner, researcher, and decision maker take a more interdisciplinary approach to engineering in the fractured rock environment. This report describes how existing tools-some only recently developed-can be used to increase the accuracy and reliability of engineering design and management given the interacting forces of nature. With an interdisciplinary approach, it is possible to conceptualize and model the fractured rock environment with acceptable levels of uncertainty and reliability, and to design systems that maximize remediation and long-term performance. Better scientific understanding could inform regulations, policies, and implementation guidelines related to infrastructure development and operations. The recommendations for research and applications to enhance practice of this book make it a valuable resource for students and practitioners in this field.
Author:
Publisher:
ISBN:
Category : Aquifers
Languages : en
Pages : 19
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Book Description
Nearly a decade of intensive geophysical logging at fractured rock hydrology research sites indicates that geophysical logs can be used to identify and characterize fractures intersecting boreholes. However, borehole-to-borehole flow tests indicate that only a few of the apparently open fractures found to intersect boreholes conduct flow under test conditions. This paper presents a systematic approach to fracture characterization designed to define the distribution of fractures along boreholes, relate the measured fracture distribution to structure and lithology of the rock mass, and define the nature of fracture flow paths across borehole arrays. Conventional electrical resistivity, gamma, and caliper logs are used to define lithology and large-scale structure. Borehole wall image logs obtained with the borehole televiewer are used to give the depth, orientation, and relative size of fractures in situ. High-resolution flowmeter measurements are used to identify fractures conducting flow in the rock mass adjacent to the boreholes. Changes in the flow field over time are used to characterize the hydraulic properties of fracture intersections between boreholes. Application of this approach to an array of 13 boreholes at the Mirror Lake, New Hamsphire site demonstrates that the transient flow analysis can be used to distinguish between fractures communicating with each other between observation boreholes, and those that are hydraulically isolated from each other in the surrounding rock mass. The Mirror Lake results also demonstrate that the method is sensitive to the effects of boreholes on the hydraulic properties of the fractured-rock aquifer. Experiments conducted before and after the drilling of additional boreholes in the array and before and after installation of packers in existing boreholes demonstrate that the presence of new boreholes or the inflation of packers in existing boreholes has a large effect on the measured hydraulic properties of the rock mass surrounding the borehole array.
Author: David Yoxtheimer
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Book Description
Fractured bedrock aquifers are key sources of potable groundwater globally. Therefore it is important to characterize the presence and orientations of subsurface fractures that impact groundwater flow in order to develop, manage and protect these critical water resources. A significant challenge in characterizing groundwater flow in a fractured bedrock aquifer is determining if anisotropic conditions exist. The square array method provides a means to estimate geo-electrical anisotropy, which can be useful when conducting hydrogeologic investigations including mapping fracture orientations, siting water supply wells, conducting source water protection programs, or mapping contaminant plumes. However, this method has not been previously tested to characterize the hydrogeology of folded and fractured carbonate bedrock overlain by conductive layers of soil and epikarst, nor for characterizing shale formations. In this study, the square array method is used to measure the change in electrical resistivity of the subsurface with respect to azimuth at six locations in the Cambrio-Ordovician carbonate bedrock aquifer of Spring Creek watershed and the shale formation underlying the Susquehanna Shale Hills Critical Zone Observatory (SSHCZO), both located within the Appalachian Valley and Ridge Province of central Pennsylvania. The carbonate bedrock aquifer is mantled with residual soils consisting primarily of silt and clay loams of variable thickness (0 to greater than 10 meters) below which occurs an epikarst system that plays a significant role in shallow groundwater flow. The square array is used to characterize the carbonate aquifers bedrock strike- and fracture-related anisotropy and provide estimates of secondary porosity. The results show that the square array apparent resistivity data correlates well with known bedrock structure, in particular the resistivity minima for the deeper measurements (40- and 50-meter a-spacings) are coincident with the northeast-southwest orientation of bedrock strike and/or mapped fractures, where present. In addition, estimates of secondary porosity from the square arrays 40- and 50-meter a-spacings (range of 0.7-4.4% with a mean of 3.1%) generally compare favorably to independent estimates of bedrock structure and secondary porosity from outcrop measurements and groundwater level/streamflow recession data (1-5%). The results of this study demonstrate that the square array method can be used effectively in complex, fractured carbonate bedrock settings to characterize bedrock anisotropy and secondary porosity, which were field-validated based on bedrock outcrop structure and fracture geometry measurements. Previous square array studies have detected anisotropy and estimated secondary porosity in both carbonate and crystalline bedrock, however this research further validates the method by comparing field measurements to the square array data, and thus advances the methods application. Geo-electrical anisotropy associated with inclined bedding planes and fractures in bedrock is often not factored into apparent resistivity results, much less data inversion, which can lead to misleading model results. In particular, the paradox of anisotropy occurs where collinear resistivity data are collected in areas with inclined bedding planes or fractures and longitudinal apparent resistivity is greater than transverse apparent resistivity, which is the converse of when true resistivity values are considered. The SSHCZO study expands critical zone research by evaluating the effects of anisotropy on earth resistivity measurements in a fractured shale bedrock setting using both square and Wenner arrays. The square array can be used to determine the magnitude and orientation of anisotropy, as it is not subject to the paradox of anisotropy, whereas collinear arrays are, including the Wenner array. In fractured shale bedrock the anisotropy effects can be significant, including the paradox of anisotropy, which can lead to significantly inaccurate models if not factored into the input data. In this study the square array was used to evaluate site anisotropy at variable depths, including through the soils and bedrock profile, including fractured, weathered and unweathered bedrock intervals. The square arrays anisotropy coefficient was then factored into apparent resistivity data from strike parallel and perpendicular 2-D Wenner arrays to correct for the paradox of anisotropy. The corrected 2-D resistivity data were then inverted to obtain model results where longitudinal resistivity values were lower than transverse resistivity values, as would be expected. In addition, a series of ten parallel 2-D Wenner arrays were run and used to create pseudo 3-D models of the sites resistivity distribution using anisotropy corrections from the square array data for comparison to 3-D models without this correction. This sequence of steps resulted in a 3-D resistivity model that provided useful insights into shallow groundwater interflow at the SSHCZO site. Ultimately this study provides a method that can be applied to geophysically characterize the groundwater flow mechanisms in the critical zone and allow investigators to design subsurface monitoring programs to further advance hydrologic and hydrogeologic research. The combined results of these studies show the square array can be utilized in fractured carbonate and shale bedrock settings to ascertain geo-electrical anisotropy, which correlates well to bedrock and fracture strike. For the fractured carbonate aquifer the square array was validated to provide reasonable estimates of secondary porosity based on both outcrop fracture measurements and groundwater level recession analysis. In the shale bedrock setting, the square array provided a useful correction factor for the coefficient of anisotropy in 2-D collinear resistivity arrays, which then yielded useful insights into shallow groundwater flow conditions via 3-D modeling developed from the corrected 2-D resistivity arrays.
Author: Matthew C. Cole
Publisher:
ISBN: 9780355669749
Category : Groundwater flow
Languages : en
Pages : 94
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Book Description
Abstract: A better understanding of groundwater flow through bedrock fractures is critical to applications involving heat and solute transport. Pumping tests performed to characterize these systems are often ill-suited because the radius of penetration quickly expands beyond the inter-well distance, gaining information beyond the well pair of interest. Periodic hydraulic tests allow the radius of penetration to be controlled by the frequency of oscillation, and testing at multiple frequencies gives parameter estimates for a range of spatial scales. Periodic pumping tests were performed at the Mirror Lake experimental fractured rock hydrology field site in New Hampshire. Results suggest a more complex, 3D network of connectivity than previously indicated by constant rate pumping tests. The relative degree of connectivity, given by diffusivity, corresponds to early-time response seen in the constant rate test. This confirms that the periodic tests investigated at a smaller penetration radius than the steady response from constant pumping.
Author: Neil Flahive
Publisher:
ISBN:
Category : Electronic dissertations
Languages : en
Pages :
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The water levels and water quality obtained from open borehole wells in fractured bedrock are flow weighted averages that are a function of the hydraulic heads and transmissivities of water contributing fractures, which are rarely known. Without such knowledge using water levels and water quality data form fractured bedrock wells to assess contaminant conditions can be highly misleading. This study demonstrates a cost effective single packer fracture characterization method that can be used in fractured bedrock to determine the hydraulic heads and transmissivities of individual fracture zones. The method entails inflating a pipe plug to isolate sections of an open borehole at different depths and monitoring changes in water level with time. At each depth, the change in water level with time was used to determine the sum of fracture transmissivities above the packer and then to solve for individual fracture transmissivity. Steady state heads along with the transmissivities were used to determine fracture heads by solving for individual heads using the weighted average head equation. The method was tested in five wells in crystalline bedrock located at the University of Connecticut in Storrs. The wells had been previously logged with both conventional logging methods and the dissolved oxygen alteration method. The single packer head and transmissivity results were found to agree with borehole flow conditions determine by these other methods.
Author:
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Category :
Languages : en
Pages :
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Book Description
The analysis of fluid flow through fractured rocks is difficult because the only way to assign hydraulic parameters to fractures is to perform hydraulic tests. However, the interpretation of such tests, or ''inversion'' of the data, requires at least that we know the geometric pattern formed by the fractures. Combining a statistical approach with geophysical data may be extremely helpful in defining the fracture geometry. Cross-hole geophysics, either seismic or radar, can provide tomograms which are pixel maps of the velocity or attenuation anomalies in the rock. These anomalies are often due to fracture zones. Therefore, tomograms can be used to identify fracture zones and provide information about the structure within the fracture zones. This structural information can be used as the basis for simulating the degree of fracturing within the zones. Well tests can then be used to further refine the model. Because the fracture network is only partially connected, the resulting geometry of the flow paths may have fractal properties. We are studying the behavior of well tests under such geometry. Through understanding of this behavior, it may be possible to use inverse techniques to refine the a priori assignment of fractures and their conductances such that we obtain the best fit to a series of well test results simultaneously. The methodology described here is under development and currently being applied to several field sites. 4 refs., 14 figs.
Author: Mishal Mansour Al-Johar
Publisher:
ISBN:
Category :
Languages : en
Pages : 0
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Book Description
Open and connected fractures, where present, control fluid flow and dominate solute transport. Flow through fractures has major implications for water resource management, underground waste repositories, contaminant remediation, and hydrocarbon exploitation. Complex fracture morphology makes it difficult to quantify and predict flow and transport accurately. The difficulty in usefully describing the complex morphology of a real fracture from a small 3-D volume or 2-D profile sample remains unresolved. Furthermore, even when complex fracture morphology is measured across three-dimensions, accurate prediction of discharge remains difficult. High resolution x-ray computed tomography (HXRCT) data collected for over 20 rock surfaces and fractures provide a useful dataset to study fracture morphology across scales of several orders of magnitude. Samples include fractured rock of varying lithology, including sandstone, volcanic tuffs and crystalline igneous and metamorphic rocks. Results suggest that the influence of grain size on surface roughness is not readily apparent due to other competing variables such as mechanics, skins and coatings, and weathering and erosion. Flow tests of HXRCT-scanned fractures provide real discharge data allowing the hydraulic aperture to be directly measured. Scale-invariant descriptions of surface roughness can produce constrained estimates of aperture variability and possibly yield better predictions of fluid flow through fractures. Often, a distinction is not made between the apparent and true fracture apertures for rough fractures measured on a 2-D topographic grid. I compare a variety of local aperture measurements, including the apparent aperture, two-dimensional circular tangential aperture, and three-dimensional spherical tangential aperture. The mechanical aperture, the arithmetic mean of the apparent local aperture, is always the largest aperture. The other aperture metrics vary in their ranking, but remain similar. Results suggest that it may not be necessary to differentiate between the apparent and true apertures. Rock fracture aperture is the predominant control on permeability, and surface roughness controls fracture aperture. A variety of surface roughness characterizations using statistical and fractal methods are compared. A combination of the root-mean-square roughness and the surface-to-footprint ratio are found to be the most useful descriptors of rock fracture roughness. Mated fracture surfaces are observed to have nearly identical characterizations of fracture surface roughness, suggesting that rock fractures can be sampled by using only one surface, resulting in a significantly easier sampling requirement. For mated fractures that have at least one point in contact, a maximum potential aperture can be constrained by reflecting and translating a single surface. The maximized aperture has a nearly perfect correlation with the RMS roughness of the surface. These results may allow better predictions of fracture permeability thereby providing a better understanding of subsurface fracture flow for applications to contaminant remediation and water and hydrocarbon management. Further research must address upscaling fracture morphology from hand samples to outcrops and characterizing entire fracture networks from samples of single fractures.
