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Author: Clark Thompson
Publisher:
ISBN:
Category :
Languages : en
Pages : 524
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Author: Clark Thompson
Publisher:
ISBN:
Category :
Languages : en
Pages : 524
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Author: Donald Timothy Slottke
Publisher:
ISBN:
Category :
Languages : en
Pages : 468
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Where open, connected fractures are present, they dominate both fluid flow and transport of solutes, but the prediction of hydraulic and transport properties a priori has proven exceedingly difficult. A major challenge in predicting solute transport in fractured media is describing the physical characteristics of a representative surface that is appropriate to modeling. Fracture aperture, roughness, and channeling characteristics are important to predict flow and transport in hard rock terrains. In areas with little soil cover, fracture mapping can indicate areas or directions of greater permeability but not the magnitudes. Both cover and complex geology can limit mapping. Hand samples are generally available and upscaling from their properties would be highly beneficial. Assessing the impact of roughness on field-scale fluid flow through fractured media from samples of natural fractures on the order of 100cm2 assumes a relationship between fracture morphology and discharge is either scale invariant or smoothly transformable. It has been suggested that the length scale that surface roughness significantly contributes to the discharge falls within the size of a typical hand sample, but few data exist to support extension of small-scale relationships to larger scales. I analyze the results of flow tests on a single fracture through a 60 x 30cm block of rhyolitic tuff. The results are compared with relationships of smaller samples in a similar tuffs and granites. The data are processed to yield regularly gridded surface elevations. Describing roughness as a ratio of surface area to footprint, variances of the roughnesses of surface covering equivalently sized square samples are plotted against sample size to determine if a representative surface exists. For specimens of fractures measuring up to 25 x 29cm, a 3.2 x 3.2cm sample of granite with an iron oxide/clay fracture skin yields a reasonable expression of the roughness of the entire surface. The number of data points included in a sample of this size transcends skin type, composition and grain/crystal size. The results suggest that the unmodified cubic law is valid for the range of gradients expected in the field using the geometric mean of areal aperture data to estimate hydraulic aperture. The data also indicate that fracture aperture is not well predicted by single aperture measurements or even by averaging along a particular scan line; three-dimensional laboratory analysis and/or field testing are required. There may be a suitable scale of data for upscaling fracture roughness on the order of 10cm2. However, due to mismatch between top and bottom surfaces inherent in natural fractures, aperture samples are not consistent across the specimen and cannot be scaled. Upscaling of other factors, such as flow channeling, remain to be tested.
Author:
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ISBN:
Category :
Languages : en
Pages :
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Fluid flow through rock fractures can be orders of magnitude faster than through the adjacent low-permeability rock. Understanding how fluid moves through these pathways is important for the prediction of sequestered CO2 transport in geologic reservoirs. Reservoir-scale, discrete-fracture simulators use simplified models of flow through fractures to determine transport properties in complex fracture networks. A high level of approximation is required in these reservoir-scale simulations due to the number of fractures within the domain of interest and because of the limited amount of information that can be obtained from geophysical well-logs (Long et al. (1996)). For this study, flow simulations through a CT-scanned fracture were performed to evaluate different fluid transport parameters that are important in geological flow analysis. The 'roughness' of the fracture was varied to determine the effect of the bumpy fracture walls on the fluid flow. The permeability and effective aperture were determined for flow under a constant pressure head. The fracture roughness is shown to dramatically reduce the flow through the fracture, and various relations are described.
Author: National Research Council
Publisher: National Academies Press
ISBN: 0309049962
Category : Science
Languages : en
Pages : 568
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Book Description
Scientific understanding of fluid flow in rock fracturesâ€"a process underlying contemporary earth science problems from the search for petroleum to the controversy over nuclear waste storageâ€"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: 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:
Publisher:
ISBN:
Category :
Languages : en
Pages : 566
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To quantify the roughness of natural rock fracture surfaces, a two dimensional version of the modified divider method was adopted. The parameter Dr2d9Cx was found to be suitable to quantify the roughness of natural rock fractures. In addition to the mean aperture, a modified 3D box counting method was used to quantify aperture distributions of the same fractures. The modified 3D box counting method produced fractal dimensions in the range 2.3104 to 2.5661. The following new functional relations were developed for aperture parameters: (a) power-functionally decreasing mean aperture with increasing normal stress, (b) power-functionally decreasing 3D box fractal dimension with increasing normal stress, (c) linearly increasing mean aperture with increasing 3D box fractal dimension, (d) linearly decreasing mean aperture with increasing fracture closure, and (e) linearly decreasing 3D box fractal dimension with increasing fracture closure. Fluid flow through nine natural single rock fractures was measured at different normal stresses. The flow calculated for three out of the nine fractures according to sample scale cubic law using mean apertures overestimated the experimental flow by 2.2 ̃235.0 times within a normal stress range of 0 ̃8 MPa. The elementally applied cubic law (EACL) through a finite element model (FEM) also overestimated the experimental flow by 1.9 ̃111.7 times within the same normal stress range. As the normal stress applied on a natural rock fracture increases, the overestimation increases due to increasing contact areas and increasing tortuous behavior of flow. These findings clearly show the inapplicability of the cubic law to estimate flow through natural rock fractures especially under high normal stresses. New hyperbolic functions were developed to relate mean aperture to the power n to applied normal stress at both the sample and finite element scales. The following new functional relations were developed between fluid flow rate and the aperture parameters: (a) power-functionally increasing flow rate per unit head with increasing mean aperture, (b) exponentially decreasing flow rate per unit head with increasing fracture closure, and (c) power-functionally increasing flow rate per unit head with increasing 3D box fractal dimension.
Author: Nader Fardin
Publisher:
ISBN: 9789172831391
Category :
Languages : en
Pages : 62
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Author: Hans Peter Rossmanith
Publisher: CRC Press
ISBN: 1000151387
Category : Technology & Engineering
Languages : en
Pages : 1848
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Book Description
This book focuses on the implementation and application of new concepts and methods to modelling, analysis, building, performance control and repair of structures of and in jointed rock and rock masses. It provides a forum for presentation of new research results and discussion for researchers.
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.
