Investigation of Surface Roughness of Natural Rock Fractures Using High-resolution X-ray Computed Tomography and Laboratory Flow Test Measurements PDF Download
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Author: Clark Thompson
Publisher:
ISBN:
Category :
Languages : en
Pages : 0
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Book Description
Fluid flow through natural rock fractures is an important - and often dominant - factor in many aquifer and reservoir systems. Rock fractures are rough-walled, and this surface roughness introduces complexities. The analytically-derivable 'cubic law' describes laminar flow behavior through smooth, parallel plates. Adjustment to the cubic law for surface roughness has been sought since the 1950s but remains elusive. This study evaluates the feasibility of using X-ray computed tomography (CT) to measure surface roughness of natural rock fractures. Classical roughness parameters are summarized. CT and its application to imaging fracture apertures are reviewed. The CT imaging of two natural fractures is described. The resulting 3-D surface data are analyzed using conventional statistics. Power spectral density analysis using the power law method of Brown (1995) is described and performed. The issue of spatial stationarity of the surfaces is examined. The relevant concepts from fluid mechanics are summarized. The pioneering work of Lomize (1951) and Louis (1969) is reviewed. A flow test apparatus is designed and used to test a natural rock fracture. The results of 301 flow tests are summarized and analyzed. These results are compared to the roughness correction factors of Lomize (1951) and Louis (1969)
Author: Clark Thompson
Publisher:
ISBN:
Category :
Languages : en
Pages : 0
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Book Description
Fluid flow through natural rock fractures is an important - and often dominant - factor in many aquifer and reservoir systems. Rock fractures are rough-walled, and this surface roughness introduces complexities. The analytically-derivable 'cubic law' describes laminar flow behavior through smooth, parallel plates. Adjustment to the cubic law for surface roughness has been sought since the 1950s but remains elusive. This study evaluates the feasibility of using X-ray computed tomography (CT) to measure surface roughness of natural rock fractures. Classical roughness parameters are summarized. CT and its application to imaging fracture apertures are reviewed. The CT imaging of two natural fractures is described. The resulting 3-D surface data are analyzed using conventional statistics. Power spectral density analysis using the power law method of Brown (1995) is described and performed. The issue of spatial stationarity of the surfaces is examined. The relevant concepts from fluid mechanics are summarized. The pioneering work of Lomize (1951) and Louis (1969) is reviewed. A flow test apparatus is designed and used to test a natural rock fracture. The results of 301 flow tests are summarized and analyzed. These results are compared to the roughness correction factors of Lomize (1951) and Louis (1969)
Author: John M. Sharp
Publisher: CRC Press
ISBN: 1315778823
Category : Science
Languages : en
Pages : 403
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Book Description
Understanding of groundwater flow and solute transport in fractured rocks is vital for analysis of water resources, water quality and environmental protection, geotechnical and engineering projects, and geothermal energy production. This book includes theoretical and practical analyses using numerical modelling, geochemistry, isotopes, aquifer tests, laboratory tests, field mapping, geophysics, geological analyses, and some unique combinations of these types of investigation. Current water resource and geotechnical problems and the techniques now used are also discussed. Aimed at practicing hydrogeologists, engineers, ecologists, resource managers, students and earth scientists.
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.
Author: Donald Timothy Slottke
Publisher:
ISBN:
Category :
Languages : en
Pages : 468
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Book Description
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: 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 Research Council
Publisher: National Academies Press
ISBN: 0309103711
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: American Geophysical Union. Joint Assembly
Publisher:
ISBN:
Category : Geophysics
Languages : en
Pages : 526
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Book Description
Author: Da Huo
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Book Description
Understanding multiphase fluid flow behavior in fractured porous media is crucial for developing fractured hydrocarbon reservoirs, implementing hydraulic fracturing, and predicting potential leakage in gas and CO2 storage. Since fracture aperture distributions are stress-dependent, the flow behaviors are also stress-dependent. The goal of this research is to investigate stress-dependent fluid flow properties in rock fractures. To carry out this work, fast and accurate methods to measure the stress-dependent fracture aperture and water saturation during the core-flooding experiments are needed. X-ray CT imaging is attractive for measuring fracture apertures and water saturations because it can be combined with dynamic flow experiments. In this dissertation we develop a set of methods for measuring fracture aperture and water saturation distributions and quantify the errors associated with these methods. Furthermore, we investigate the stress-dependency of fluid flow in fractures using the methods. In the first part of this dissertation, we develop a full set of methods for calculating fracture aperture and water saturation distributions using X-ray CT scanning. For fracture aperture measurements, the method relates fracture aperture with missing CT attenuation, scanner voxel size, and CT numbers of the rock matrix. The validity of the model is established by comparing apertures calculated with the conventional calibration-based method, evaluating model predictability at different scanner voxel sizes, comparing with calibration coefficients in the literature from a number of experiments with different rocks and X-ray scanners and comparing aperture measurements for air-filled and water-filled fractures. The results suggest that the method provides reliable aperture measurements. The method also avoids the need for time-consuming calibration and accounts for rock property heterogeneities. The missing CT attenuation concept is then applied to multiphase scans (scans where the fracture is partially filled with water and gas) to develop a method for measuring the water saturation in rock fractures surrounded by porous rocks. We analyze the new method by comparing water saturation measurements with two previously developed methods. The new method includes the missing CT attenuation changes for different matrix porosities and water saturations and thus it is more broadly applicable to a wide range of conditions. Finally, we quantify the systematic and random errors related to the fracture aperture and water saturation measurements. Error analysis shows the method provides an aperture measurement error of 22 microns with 5 repeated scans, which is less than one-twentieth of the voxel size. The analysis demonstrates that averaging of replicate scans highly improves the detection accuracy. Comparisons between aperture measurements made in air and water-filled fractures show that the dry scan is the most recommended method due to its lower errors. Water saturation measurements for individual pixel exhibit a high degree of error (40%). However, the average water saturation in the fracture can be measured with an accuracy of around 10% by averaging 5 repeated scans. The fracture aperture and water saturation measurement methods are particularly valuable for combining dynamic core flooding experiments with simultaneous fracture aperture and water saturation measurements. Using concurrent CT scanning and core flooding, we improve understanding of stress-dependent fluid flow in fractures. The stress-dependent permeability, capillary pressure and relative permeability in rock fractures are separately explored. From the stress-dependent permeability data, changes in permeability are attributed to three factors: changes in mean aperture, changes in roughness, and changes in contact area. We find that stress-dependent permeability and hysteretic behavior is influenced by both aperture and roughness changes. For a small aperture fracture tested here, changes in roughness dominate the permeability response to stress changes. The Modified Cubic Law (Witherspoon et al., 1980), Walsh (1981), Zimmerman et al. (1992) and Sisavath et al. (2003) models are compared with the experimental data and results show that all four models do not result in sufficiently large permeability variation. Additionally none of the previous models quantifies the relative contribution of aperture and roughness to permeability change. A new empirical model is proposed based on the Modified Cubic Law (Witherspoon et al., 1980) that provides a better match to the experimental data and accounts for both stress-dependent aperture and roughness. Using laboratory measurements of fracture aperture distributions under various conditions of effective stress, invasion percolation simulations are employed to model the capillary pressure curves as a function of the effective stress. The stress-dependent aperture distribution data demonstrates that increasing stress has two effects: (1) the mean aperture will decrease; (2) the variance of aperture distribution will increase. The mean aperture decrease will increase entry pressure. As the variance of aperture distribution increases with stress, the plateau area of the capillary pressure curve tends to grow steeper, indicating that capillary behavior changes from more fracture-like to more porous media-like. For the stress-dependency of relative permeability in rock fractures, previous studies provide contradictory evidence of the influence of increasing stress on the relative permeability of fractures. Some studies suggest that irreducible water saturation increases, while others show the reverse. In an attempt to resolve these differences, laboratory core flooding experiments are applied to measure the relative permeability of nitrogen-water mixtures in a fracture under various states of effective stress. Simultaneous X-ray CT measurements are made of aperture and water saturation distributions in the fracture. Two effective stress levels, 2.07 MPa and 5.52 MPa, are applied to investigate the stress-dependency. For both states of stress, the measurements show that the relative permeability to gas is very low until a critical saturation is reached. As gas saturation increases beyond the critical value, relative permeability to gas increases quickly while water becomes essentially immobile. Results also demonstrate that increasing stress lowers the irreducible water saturation and the end-point non-wetting phase relative permeability when the experiments are conducted at the same flow rate. Using invasion percolation theory with the fracture aperture maps made at the two different effective stresses, capillary pressure curves are calculated and used to explain changes in phase interference at different stress levels. Finally, the preferential flow paths are analyzed at both stress levels. We use this analysis to reconcile flow regimes observed in earlier studies, and conclude that the differences between them can be explained by the relative importance of viscous and capillary forces. Specifically, if the experiments are designed to keep the capillary number constant, the irreducible water saturation increases with increasing confining stress. If the experiments are conducted at the same flow rate, higher confining stress decreases the irreducible water saturation, as was observed in these experiments. The analysis and data presented here also suggest that small increases in the water saturation of a fracture may dramatically reduce gas flow rates. This may present an additional and unexplored explanation for rapid production decline of gas wells in fractured reservoirs.
Author: Jennifer Druhan
Publisher: Walter de Gruyter GmbH & Co KG
ISBN: 1501512005
Category : Science
Languages : en
Pages : 514
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Book Description
Open system behavior is predicated on a fundamental relationship between the timescale over which mass is transported and the timescale over which it is chemically transformed. This relationship describes the basis for the multidisciplinary field of reactive transport (RT). In the 20 years since publication of Review in Mineralogy and Geochemistry volume 34: Reactive Transport in Porous Media, RT principles have expanded beyond early applications largely based in contaminant hydrology to become broadly utilized throughout the Earth Sciences. RT is now employed to address a wide variety of natural and engineered systems across diverse spatial and temporal scales, in tandem with advances in computational capability, quantitative imaging and reactive interface characterization techniques. The present volume reviews the diversity of reactive transport applications developed over the past 20 years, ranging from the understanding of basic processes at the nano- to micrometer scale to the prediction of Earth global cycling processes at the watershed scale. Key areas of RT development are highlighted to continue advancing our capabilities to predict mass and energy transfer in natural and engineered systems.
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.
