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ABSTRACT: Radioactive decay heat is likely to create coupled thermal-mechanical-hydrological-chemical (TMHC) processes in the near field of a nuclear waste repository. One of the coupled TMHC processes is the effect of the rock-water interaction on fluid flow in the rock mass. This effect may also play an important role in geothermal energy recovery. Previous laboratory results showed that dissolution and re-deposition of minerals on the fracture surfaces, caused by flowing high-temperature water at a confining pressure of 5 MPa, can significantly decrease the permeability of fractured Topopah Spring tuff. The present experiment is designed to investigate the effect of differential pressure on fracture healing. Laboratory results indicate that at a differential pressure of only 0.5 MPa (confining pressure = 1 MPa, pore pressure = 0.5 MPa), the water permeability of a fractured Topopah Spring tuff sample decreased from about 18 × 10–15 m to about 11 × l0–15 m during an initial complete thermal cycle of heating to 150°C and cooling back to 25°C. Permeability decreased in the subsequent thermal cycles at greater differential pressures (1.5, 2.5, and 4.5 MPa), but the amplitudes of these decreases were much less than that in the initial thermal cycle. The permeability decrease during the initial heating is consistent with the previous results, except the amplitude of decrease in this experiment is much less than that reported previously. One possible explanation for the discrepancy is that the confming pressure in this experiment is only 20% of previous experiments. RESUME: La chaleur de desintegration radioactive induit vraisemblablement des phenomènes couples thermiques-mecaniques-hydrologiques chimiques (TMHC) au voisinage d'un site de stockage des dechets radioactifs. L'un de ces phenomènes est l'effet de l'interaction eau-roche sur la circulation de fluide dans la matrice rocheuse. Cet effet peut egalement jouer un rôle imponant dans le recouvrement d'energie geothermale. Nous avons dejà montre experimentalement que la dissolution et la redeposition de mineraux sur les surfaces de fracture, attribuables à un flux d'eau à haute temperature à une pression de confinement de 5 MPa, peut considerablement faire decroltre la permeabilite du tuf fracture à Topopah Springs. Les presents essais visent à etudier l'effet d'une pression differentielle sur le remplissage de la fracture. Les resultats experimentaux indiquent que, pour une pression differentielle de seulement 0.5 MPa (pression de confinement: 1 MPa; pression de pore: 0.5 MPa),la permeabilite à l'eau d'un echantillon de tuf fracture de Topopah Spring decroît d'environ 18.10–15 m à environ 11.10–15 m lorsque cet echantillon est soumis à un cycle thermique initial de chauffage jusqu'à l50°C, suivi d'un refroidissement jusqu'à 25°C. ZUSAMMENFASSUNG: Radioaktive Zerfallswarme fuehrt in aller Wahrscheinlichkeit zu gekuppelten thermischen, mechanischen, hydrologischen und chemischen (TMHC) Prozessen 1m Nahbereich einer Lagerstate fuer radioaktiven Abfall. Zu diesen gekuppelten TMHC Prozesse gehört u.a. die Auswirkung der Wechselwirkung von Gestain und Wasser auf den Fluessigkeitsfluβ in der Felsmasse. Diese Auswirkung kann ebenfalls eine wichtige Rolle Spielen bei der Rueckgewinnung von geothermischer Energie. Ergebnisse aus frueheren Laborversuchen zeigen daβ die Ausflösung und Wiederablagerung von Mineralien auf den Bruchoberflachen, verursacht durch Flieβwasser bei hohen Temperaturen bei einem Schwellendruck von 5 MPa, die Durchlassigkeit von gebrochenen Topopah Spring Tuffstein betrachtlich verringern kann. Das gegenwartige Experiment ist dehingehend ausgelegt, die Auswirkung von Druckunterschieden auf die Bruchstellen heilung zu untersuchen. Ergebnisse aus Laboruntersuchungen weisen darauf hin, daβ bei einem Druckunterschied von lediglich 0.5 MPa (Schwellendruck=lMPa, Porendruck=0.5 MPa) die Wasserdurchlassigkeit einer gebrochenen Topopah Spring Tuffsteinprobe wahrend eines ersten vollstandigen Warmezyklus bei Erhitzung auf 150^C und Rueckkuehlung auf 25°C von ca. 18 × 10–15 m auf ca. 11 × 10–15 m zurueckging. Wahrend die Wasserdurchlassigkeit bei den nachfolgenden Warmezyklen mit gröβeren Druckunterschieden (l,5 MPa, 2,5 MPa und 4,5 MPa) zurueckging, so war doch der Umfang dieser Rueckgange wesentlich geringer lis bei dem ersten Warmezyklus steht mit frueheren Ergebnissen in Einklang, mit Ausnahme des Umfangs des Rueckgangs, der in diesem Experiment wesentlich geringer als bereits dargestellte Rueckgange ist. Diese Diskrepanz kann möglicherweise derart erklart werden, daβ bei diesem Experiment der Schwellendruck lediglich 20% des bei frueheren Experimenten angewandten Schwellendrucks betragt.
- Geology > Mineral (1.00)
- Geology > Geological Subdiscipline > Geomechanics (0.49)
ABSTRACT: Core material was obtained from sandstones in the Natal Group, the drillhole being sunk near Kloof, Natal. Approximately 200 m of core was available and some material was taken from approximately every 10m for examination and testing. Petrographic examination of this material involved modal analysis, granulometric analysis, packing analysis and an analysis of grain contacts. The sandstones are generally fine to medium grained, subarkosic to arkosic arenites. The cement is predominantly siliceous or occasionally calcareous with a little matrix occupying the void space. The sandstones are reasonably well packed and most of the grains have either long or concavo-convex contacts. The engineering properties which were assessed included the porosity, permeability, unconfined compressive strength, point load strength, Brazilian strength, Schmidt hardness, Young's modulus and Poisson's ratio. These were determined for the same depth intervals as the petrographic examinations. In this way the influence of the petrographic properties on the engineering properties was determined. RESUME: On a obtenu Ie noyau du materiau à partir de grès du Groupe du Natal, après avoir fore près de Kloof dans Ie Natal. On a trouve environ 200 mètres de noyau et des echantillons ont ete preleves à environ tous les 10 mètres pour essais et examens. L'examen petrographique a porte sur les analyses suivantes: modale, granulome trie, tassement et contacts des grains. Les grès sont generalement forme s de grains fins ou moyens, allant d'arenites subarkosic et arkosic. Le ciment est principalement siliceux, avec du calcaire par ci par Ià, et une matrice occupant la partie vide. Les gres sont relativement bien tasses at la plupart des grains offrent un contact long ou concaveconvex. On a etabli les proprietes techniques suivantes de porosite, de permeabilite, d'effort de compression libre, de force de charge sur un point, de force Bresilienne, de durete Schmidt, de ratio de Poisson et de coefficient d'elasticite. Celles-ci ont ete determinees aux mêmes intervals de profondeur comme les examens petrographiques. C'est ainsi qu'on a determine I'influence des proprietes petrographiques sur les proprietes techiques. ZUSAMMENFASSUNG: Corematerial wurde von Sandstein in der Natal Gruppe gewonnen, das Drill-Loch wurde angebracht in der Nahe von Kloof in Natal. Etwa 200 Meter Corematerial wurde gewonnen, davon etwa aile 10 Meter Proben fuer Untersuchungen und Tests entnommen. Petrographische Untersuchungen dieses Materials' beinhaltete die Modal Analyse, granulometrische Analyse, Pack Analyse und eine Analyse ueber die Strukturbeschaffenheit. Sandgestein is im a1lgemeinen fein bis halbfein in der Struktur, subarkosic bis arkosic arenites. Der Zement ist vorherrschend siliceous oder gelegentlich calcareous mit etwas matrix in den Öffnungen. Sandgestein ist ziemlich kompakt und die meisten Sandkörner haben entweder langen oder concavo-convex Kontakt. Die geo-technischen Eigenschaften, die untersucht wurden, bc;inhalteten Porösitat, Wasserdurchlassigkeit, offene Druckstlirke, Punktladestarke, Brazilianische Starke, Schmidt Harte, Young's Modulus dnd Poisson's Ratio. Diese Untersuchungen wurden in denselben Abstanden angewandt wie die petrographischen Untersuchungen. Auf diese Weise wurde der Einfluβ der petrographischen Eingenschaften auf die geo-technischen Eigenschaften festgestellt. INTRODUCTION This investigation was carried out on sandstone of the Mariannhill Formation of the Natal Group. The boundary between the former two formations is gradational, being marked by a decrease in grain size, increased mica content and the occurrence of carbonate nodules. The maximum thickness of the Mariannhill Formation amounts to 400 m. These sandstones are reddish-brown in the lower part of the formation, becoming pinkish coloured in the upper horizons. The overlying Westville Formation is distinguished from the Mariannhill Formation by the presence of pebbles and cobbles. Argon40- Argon39 dating of the Natal Group gives an approximate age of 490 Ma (Thomas et ai, 1992). In other words these sandstones are of early Ordovician age.
- Europe > Norway > Norwegian Sea (0.44)
- Africa > South Africa (0.40)
- Geology > Rock Type > Sedimentary Rock > Clastic Rock > Sandstone (1.00)
- Geology > Geological Subdiscipline > Geomechanics (1.00)
ABSTRACT: The modeling of flow and transport in fractured rock masses has been done deterministically or statistically, using either discrete or continuum representations, but transport through fractured rocks cannot be considered as fully understood yet. Even flow in a single fracture cannot be modeled realistically. This paper will review the recent modeling concepts for fractured rocks and shows how to determine permeability coefficient for rock masses by using direct measurement, inverse analysis and numerical techniques. Chemical transport modeling for fractured rock is described in simple terms and the parameters to be obtained for the analysis are examined in relation to the flow modeling. Zusammenfassung: Die Modellierung von Flieβ- und Transportproblemen im gekluefteten Gebirge wurde bislang entweder deterministisch oder statistisch mit diskreten bzw. kontinuierlichen Ansatzen durchgefuehrt. Transportprobleme durch geklueftetes Gebirge sind allerdings noch nicht vollstandig erforscht. Eine realistische Modellierung gelingt noch nicht einmal fuer eine einzelne Kluft. In diesem Beitrag werden neuere Modellierungskonzepte vorgestellt. Weiterhin wird aufgezeigt, wie Durchlassigkeitsbeiwerte fuer geklueftetes Gebirge mithilfe direkter Messungen, inverser Methoden und numerischen Techniken hergeleitet werden können. Enfache Ansatze zur Modellierung chemischer Transportvorgange im klueftigen Gebirge werden beschrieben. Die Eingangsparameter, die fuer die Analyse notwendig sind, werden in ihrem Bezug auf die Modellierung untersucht. RÉSUMÉ: La modèlation de I' ecoulement des fluides et la modèlation du transport dans une masse de roches fracturees à ete faite de façon deterministe et statistique. Aujourd'hui, Ie transport à travers des roches fracturees ne peut pas être considere comme entièrement maitrise. De même, I'ecoulement des fluides dans une discontinuite ne peut pas être modele tout à fait realiste. Pour des roches fracturees, ce papier reverra les concepts de modèlation recents et presente aussi differentes manières comme la mesure directe, I'analyse inverse et des techniques numeriques pour determiner Ie coefficient de permeabilite. La modèlation du transport chimique dans des roches fracturees est decrite de façon simple et les parametres necessaire dans I'analyse sont examines en relation avec Ie modèle de I' ecoulement. 1. INTRODUCTION Considering the stability of rock slopes, that of large dams and the stability of tunnel for road, aqueduct, a compressed air energy storage system, it is the fluid pressure itself which is of main interest. In other areas such as the disposal of radioactive or toxic industrial waste and in case of the storage of oil and LNG in unlined and lined rock chambers, the focus is on the percolation of fluid which transport the contamination material. Although it is very difficult task, the estimation of the influences of water flow on the systems or the environment is one of the subjects to be examined thoroughly in the field of rock mechanics. Fig. 1 shows an typical approach to obtain solutions and predictions for rock hydraulic problems. Research and development in rock mechanics start from site investigation, tests and measurements at the field. These data must be converted into a rock model and will be evaluated at the different stages. Fluid flow through the rock mass is basically determined both by the properties of the intact rock and of the discontinuities. In practice, the intact rock - with exceptions - has limited ability to transmit fluids, discontinuities are dominant and fluid flow occurs mainly through discontinuities. Then the hydraulic behavior of the rock mass is determined by the geometry of the fracture or discontinuity system. Geometry data of rock fractures are usually collected from one or two dimensional scanline surveys or cell mappings of borehole cores, exposures and tunnel walls, by individual engineers or geologists. Although it is an inexact method of data collection, reliability can be increased by statistical and probabilistic methods.
New Measuring System And High Speed Three Dimensional Inversion Method For Hydropulse Tomography
Masumoto, Kiyoshi (University of Tokyo) | Tosaka, Hiroyuki (University of Tokyo) | Kojima, Keiji (University of Tokyo) | Itoh, Kazumasa (Oyo Corporation, Tokyo) | Otsuka, Yasunori (Oyo Corporation, Tokyo)
ABSTRACT: For identifying three dimensional permeability distribution in rock mass, the authors proposed Hydropulse Tomography System consisting of field measurement system and numerical inversion software. In this paper, the authors present newly developed field measurement system for multiple points in multiple boreholes, and high speed numerical inversion code with laboratory and field applications. RESUME: Pour l'identification de la distribution de permeabilite à trois dimensions dans la masse de ruche, les auteurs ont propose Ie Système de Tomographie Hydropulsation comprenant Ie système de mesure de champ te Ie logiciel d'inversion numerique. Dans ce document, les auteurs decrivent Ie système de mesure de champ developpe recemment pour les points multiples dans les trous de sondemultiples, et Ie code d'inversion numerique à haute vitesse. ZUSAMMENFASSUNG: Zur Identifizierung von dreidimensionaler Permeabilitatsverteilung in Gesteinsmassen schlagen die Autoren ein Hydroimpulse-Tomografie-System vor, bestehend aus einem Feldmessungssystem und numerischer Inversionssoftware. In disser Schrift beschreiben die Autoren ein neu entwickeltes Feldmessungssystem, fuer mehrfache Punkte in mehrfachen Bohrlöchern und einen schneUen Code zur numerischen Inversion. 1 INTRODUCTION For utilization of rock mass to foundation of large scale structures such as dam, underground power plant, cavern for oil or gas storage, the characterization effort requires effective field measurement and analysis methods to determine hydraulic properties, especially the degree of inhomogeneity in the rock. For this purpose, the authors have been proposing Hydropulse Tomography, which consists of measuring system of transient pressure response caused by injection and/or pumping of fluid into/from underground rock mass, and numerical inversion of permeability distribution from these transient data. And, Hydropulse Tomography measuring and analyzing system enables us to acquire three dimensional hydraulic information with relatively small number of boreholes compared with conventional hydraulic testings. In this paper, newly developed multi-well multi-point pressure measuring system and high speed numerical inversion method will be described. 2 MEASURING SYSTEM 2.1 Basic concept In actual site investigation, pressure due to the injection at injection interval in injection borehole is transmitted to receiving borehole in rock mass, according to 3-D permeability distribution. And, as the distance between injection and receiver boreholes increases, the response in receiving section becomes smaller. For receiver device, quartz oscillating pressure transducer is attached. This pressure transducer has resolution of l.0X10–8 FS under 2,000,psia measuring range. An example of injection and receiving borehole arrays is shown in Figure 1, and one of obtained pressure performances in injection and receiving sections is shown in Figure 2. In this example, distance between injection and receiving boreholes is 36.5m. However, pressure response of about l0cm H20 was measured with about 7 kgf/cm injection pressure. In this application, 4 sets of quartz oscillating pressure transducer were attached to the receiver device, which was developed as a prototype in 1990 by the authors for field investigation. On the other hand, number of receiving sections in receiving boreholes is 16, set by changing measuring interval and repeated injection at same injection borehole. This operation expended much time in measurement and is not preferable for Hydropulse Tomography because of the effect of changing hydraulic conditions of objective region, which would be treated as boundary condition in numerical inversion. And, hydraulic properties of rock mass around injection borehole might also be disturbed by repeated injection at same interval. 2.2 New measuring system In order to eliminate the effect mentioned above and make it cost effective, number of receiving points where response pressure performance can be measured at one time should be many as possible. For this reason, the authors have developed multi-well multi point pressure measuring system as receiver device.
ABSTRACT: The first topic of the paper describes the "in-situ" directional (3-D) hydraulic conductivity tests performed to evaluate the permeability tensor of the metapellites in the abuttment of Pirapora Dam, Brazil. Polar diagrams are used in the analysis and data relative to direction and inclination of the hydraulic conductivity tensor are showed. The second topic is concerned to the result of the same kind of tests performed after cement grout is injected into the borehole with the objective to analyse the grouting efficiency. A dislocation in the hydraulic conductivity tensor and modified anisotropy relation was founded after grouting. RESUME: La première partie du travil decrit les resultads des essays hydrauliques 3-D pour evaluer le tenseur de conductivite hydrauliques des metapelites de l'abuttment droite du barrage de Pirapora, Bresil. Les resultants, representes p.r diagrams polaires, montrent la direction et le pendage du tenseur de conductivite hydraulique du massif rocheux "in natura". Les auteurs on verifie entre les resultats des premiers essays et des essays suivants, une dislocation du tenseur, conditioniee par des changes dans la geometrie de les familes de fractures. ZUSAMMENFASSUNG: Im ersten Teil des Beitrags Werden die von den Autoren ausgefuehrten gerichteten (3-D) Durchlassigkeitsversuche beschrieben mit denen der Durchlassigkeitstensor der teilentfestigten Gesteine am Widerlager des Pirapora Dammes, Brasilien, ermittelt wurde. Die Ergebnisse werden in Polar-Diagrammen dargestellt, aus denen Richtung und Neigung des Durchlassigkeitstensors entnommen werden konnen. Danach werden im zweiten Teil die neuen Ergebnisse gezeigt, die mit der gleichen Versuchsart im gleichen Gebirgemassiv nach dem Injizieren gewonnen warden, um den Injektionserfolg im untersuchten Gebirge zu ermitteln. Die von den Autoren erarbeiteten Schlussfolgerungen zeigten, dass im hydraulischen Durchlassigkeitstensor der Felsmasse vor und nach denm Injizieren ein Unterschied besteht. So wurde eine örtliche Versetzung des Tensors festgestellt und in Beziehung gebracht zu der auf der Baustelle ermittelten Kluftlachengeometrie. 1 INTRODUCTION The "in-situ" definement of hydraulic parameters in rock masses have a considerable interest for most of the projects related to power plants, caverns, study of transport or particles and subterraneous work in general. In modern times, project needs and the importance of hydraulic parameters are related not only to the stability analysis but also to the environmental requirement. Within this context Rock Hydraulic appears as an important discipline whose concepts are applied in the majority of the works in rocks. In Brazil, the experience of the Institute of Technological Research of São Paulo (IPT) to collect hydraulic data in rock masses was first connected to the foundations of big power plants built in the seventie's. However, since the start of the eigthie's, this exprience has been enlarged to appliance in subterranoeus work in general including work donne in mining engineering and tunneling. Following this experience, a campaign of hydraulic 3-D and single tests was performed by the authors to study the grouting efficiency in the right abuttment of Pirapora dam, owned to the Electrical Company of São Paulo (ELETROPAULO). The results of both the geological survey to determine the geometrical parameters of the main fractures families and the hydraulic 3-D and single tests executed in the rock mass volume studied are showed and discussed in the paper. The first phase of investigations is concerned to the rock mass "in natural". Geological survey and hydraulic tests were performed with the objective to determine the reference parameters in the rock mass. The second phase is referred to the execution of the same test after the cement grout is injected into the boreholes.
A Non-pressurized Grouting Method Using Clay For Controlling Groundwater Around Crude Oil Storage Caverns
Miyanaga, Yoshiharu (Electric Power Development Co., Ltd) | Ebara, Masahiko (Electric Power Development Co., Ltd) | Kojima, Keiji (The University of Tokyo) | Makita, Toshiaki (Japan Underground Oil Storage Co., Ltd) | Tokimasa, Hiroshi (Ministry of Construction)
ABSTRACT: In one rock cavern for crude oil storage with the water barrier system, clay grouting (non-pressurized clay grouting) method was employed in order to control groundwater and to reduce an amount of seepage flow. Before applying this method to the construction, indoor and in-situ tests were performed to confirm clay clogging mechanism and effects of clay grouting. RESUME: Dans une cavite dans la roche destinee au stockage du petrole brut avec le système de barrière d'eau, une methode de stabilisation du sol par argile (stabilisation par argile sans pression) a ete employee afin de contrôler les eaux souterraines et reduire le volume des infiltrations. Avant d'appliquer cette methode à la construction, des essais en laboratoire et sur Ie terrain ont ete realises pour verifier Ie mecanisme de colmatage à l'argile et les effets de stabilisation du sol par argile. ZUSAMMENFASSUN: In einer Felsbetthöhle fuer Rohöllagerung mit Wasserstausystem wurde ein druckloses Toninjektionsverfahren zur Grundwasserkontrolle und Reduzierung von Sickerströmung angewendet. Vor der praktischen Anwendung wurden im Labor und am Ort Pruefungen ausgefuehrt, um den Tonverschluβmechanismus und die Wirkung der Toninjektion sicherzustellen. INTRODUCTION: In Japan, the construction of underground crude oil storage plants (3 sites - 5 million kiloliters) for national petroleum stockpiling was started in 1987, and all plants were completed in 1994. At present, oil installation has also been completed. The water barrier system is employed to prevent leakage of oil and petroleum gas at these three storage plants. The bedrock of the Kuji site, one of the three sites, consists of granite, but this is considerably fractured, and the average permeability coefficient is very large, (7.6 × 10–8 m/sec). Accordingly, difficulty in the construction due to excessive water leakage had been anticipated. However, in case extensive drawdown of groundwater level around caverns occurred during construction, it might be difficult to raise the groundwater table again after completion. Furthermore, remained unsaturated zone around caverns has possibility to invalidate functions of the artificial water barrier. Therefore, the caverns were excavated under the active water barrier system in order to prevent the excessive drawdown of groundwater level. In addition to this, it was necessary to reduce the amount of seepage in order to decrease the operation cost for wastewater disposal system after completion. Considering the above-mentioned requirements, the non-pressurized clay grouting method was employed, using the seepage flow from water barrier system to the caverns. Since the effect of the clay grouting has been confirmed, an outline of the process and its results are reported in this paper. 1. CLAY GROUTING Generally, grouting means pressurized injection of hardening materials such as cement into cracks around boreholes. On the other hand, clay grouting stated hereafter is a non-pressurized grouting utilizing seepage flow directed toward caverns. Clay particles carried into fissures or fractures by seepage flow plug those flow path slowly and widely. As a result impermeability of extensive rock mass including caverns can be uniformly improved. Concretely speaking, clay grouting is accomplished in the following way. First, water barrier tunnels and water barrier boreholes are excavated prior to excavating the storage caverns. Then, while the caverns are being excavated, water is poured into the water barrier facilities in order to prevent the groundwater level from falling excessively. In the clay grouting method, clay is mixed with this water and applied to the rock through the water barrier facilities. The sequence of cavern excavation is as follows:the top heading, arch enlarging, first stage bench cut, second stage bench cut, third stage bench cut.
- Reservoir Description and Dynamics > Storage Reservoir Engineering > Natural gas storage (0.61)
- Reservoir Description and Dynamics > Reservoir Fluid Dynamics > Flow in porous media (0.55)
- Health, Safety, Environment & Sustainability > Environment > Water use, produced water discharge and disposal (0.54)
ABSTRACT: A tomography-type injection test was carried out using a 30 cm cube of naturally fractured chert block. A total of more than 900 flow rate and pressure data were used for inverse analysis and a three dimensional permeability profile was obtained. The results showed that the permeability and flow rate extend over a wide range. It is suggested that a small number of localized paths are controlling the overall flow pattern inside the sample. Tracer tests were also carried out to examine the transport characteristics. Tracer breakthrough was observed at limited number of areas supporting the existence of the localized flow paths. This was consistent with the results from the particle tracking simulations. RÉSUMÉ: L'essai d'injection tomographique a ete efectue sur un block de silex noir de 30 cm ayant des fissures naturelles. Plus de 900 donnees au total concernant Ie debit et la pression ont ete utilisees pour l'analyse inverse et la courbe de permeabilite tridimensionalle a ete obtenue. Les resultats ant montre que permeabilite et Ie debit presentent une grande variation. II est suggere qu 'un nombre limite de courants localises determinent la configuration generale des courants à l'interieur de I'echantillon. Par ailloeurs, des essais à la solution de depistage ont ete faits pour examiner Ie comportment caracteristique. La solution n'a debouche qu'à un certain nombre de portions justifiant l'exsistence de courants localises. Cesi correspond aux resultants de la simulation de depistage aux paricules, ZUZAMMENFASSUNG: Mit einem 30-cm-wuerfel aus natuerlich gebrochenem kieselschiefer wurde eine tomographische injektionspruefung ausgefuerhurt. Fuer inverse analyse und ein dreidimensionales permeabilitatsprofil wurden ueber 900 fluβraten und druckdaten erhalten. Die ergebnisse zeigten, daβ sie permeabilitat und fluβrate ueber einen groβen bereich variieren. Es wird vermutet, daβ eine kleinen anzahl lokalisierter bahnen das gesamtfluβbild in der probe bestimmt. Zur weiteren unterscuchung der transporteigenschaften wuden tracer-tests ausgefuert, wobei in einer begrenzten anzahl von bereichen tracer-durchbruch beobachtet wurde, was auf das vorhandensein lokalosierter bahnen schlieβen laβt. Dies stand im einklang mit den ergebnissen aus partikel verfolgungs simulationen. 1 INTRODUCTION: Understanding fundamental mechanisms of fluid and mass transport through fractured rocks is becoming more and more important not only from water resources or reservoir engineering points of view but also for the performance assessment of a geological disposal high-level nuclear wastes. Because of its heterogeneous nature, flow in a fractured rock is highly complex and difficult to predict. In the past two decades, considerable amount of effort has been devoted in developing numerical models (Long et. al. 1984, Dershowitz et. al, 1991) and obtaining field data (Olsson 1992). These results suggest that channeling is considered to be one of the controlling mechanisms for fluid and mass transport. This paper describes a numerical and laboratory study to clarify the flow structure and its influences on flow and transport in such a heterogeneous and discontinuous rock. 2 EXPERIMENTAL PROCEDURES 2.1 Basic concept of the experiment The authors have developed a laboratory technique to obtain a three dimensional permeability profile in a heterogeneous rock (Shimo et. al. 1994). In this technique, which is based on the concept of tomography, a lattice shape gasket is attached on each face of a sample to create multiple windows for fluid injection or withdrawal. As shown in Figure 1, the gasket is composed of a sealing element made of silicon rubber and a plastic plate. By pressing this gasket against each face of a sample using hydraulic or mechanical pressure, each of the windows, or panels, created by the sealing element is hydraulically isolated one from another.
ABSTRACT: An attempt to inventarise research activities in the field of contaminant transport through fractured rock is made viewed from a European perspective. Recent trends and alternatives are reviewed. The problem of model verification and validation is critically discussed. RESUMÉ: Une discussion a lieu actuellement sur les activites de recherche dans Ie domaine du transport des contaminants dans les roches fracturees et ce avec une perspective Europeenne. Les tendances recentes aussi que les autres conception sont debattues, Le thème de la verification et de la validation des modèles est egalement passe en source de façon critique. ZUSAMMENFASSUNG: Es wird versucht die Forschungsaktivitaten im Bereich der Schadstoffausbreitung in klueftigem Festgestein aus europaischer Sicht zusammenzufassen. Alternative Ansatze und aktuelle Trends werden vorgestellt. Das Problem der Verifikation und Validierung von Modellen wird kritisch diskutiert. INTRODUCTION Considerable research has been carried out to understand, describe, and model the migration of contaminants through porous media with the aim to predict their transport in space and time. Basic laws of water flow through porous aquifer systems and numerical methods have been established. Porous media transport is now a research topic with a structured and well defined theoretical basis. Transport through fractured rock, on the other hand, cannot be considered as fully understood yet. Considering the continuum or discontinuum approaches (Bear, 1993) when dealing with ground water flow in fractured rock and further that the fractured mass is generally speaking hydraulically not equivalent to a porous medium, than the flow must be described in relation to individual fractures and fracture sets. This gives rise to several ways of looking at the problem ranging from the classical analytical solution for the transport problem in a single fracture to multiple flow in fracture sets using numerical attempts (such as the double porosity model or joint-matrix-models), from stochastic approaches (such as invariant probability concepts, percolation models, or random walk concepts) to alternative ideas like the application of the chaos theory (fractal dimension) to transport phenomena. All these approaches have advantages and disadvantages, they apply to certain boundary conditions and levels of generalisation. One key aspect of this discussion is the scale: as long as we carry out our analysis in a so-called Representative Elementary Volume (REV) (Bear 1972, Bachmat & Bear 1985) of the porous domain considered we may adopt generalised solutions. However, it is not clear whether REV can also be defined in fractured rocks mass. Still open questions of qualitative and quantitative nature are due to the characterisation of fracture flow (that will be affected by the individual fracture or fracture set itself, fracture orientation, density, aperture opening, channelling, degree of fracture connectivity and conductivity), the mass transport processes (advection, dispersion), and the chemical, biological, and radioactive processes influencing the contaminant transport (such as sorption reactions, redox-reactions, hydrolysis reactions, complexation, biodegradation, radioactive decay etc.). This variety of parameters makes this research area a quite exciting and challenging topic. This paper looks upon some selected work that has been done so far from an European prospective with the aim to be a quo vadis-paper, analysing recent tendencies of research activities concerned with transport in fractured media. Finally, the problem of model verification and so called "validation" will be discussed and the question of uncertainty will be raised: uncertainty in the models, uncertainty in the parameters and data and consequently uncertainty in the results of modelling contaminant transport. EUROPEAN RESEARCH During the past decade, research activities devoted to characterise and model flow and contaminant transport through fractured rocks has been receiving an increasing attention. A reason for that is probably the fact that several countries of Europe consider todays' storage facilities in deep geological formation, e.g. in crystalline bedrock, at depths of 500 m or more as final repositories for mainly high level radioactive waste and in some cases also for chemotoxic waste.
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- North America > United States > Arizona (0.28)
ABSTRACT: This paper presents a mathematical formulation where the solute concentrations between the fractures and the matrix have been expressed separately but related through an exchange function. A radial flow configuration and an average flow velocity are assumed. The convective fluid motion caused by density differences as a result of temperature variations are also considered. The transient heat flow is evaluated to determine the specific heat flux. The result is subsequently cast in the transport equation to evaluate the concentration changes. Solutions representing transient heat flow and solute transport along with steady fluid flow in fractured rock masses are derived, and important influence of the thermal coupling on solute transport is identified. RESUME: Cette communication presente une approche mathematique dans laquelle les concentrations du solute existant dans les fractures ainsi que dans la matrice rocheuse ont ete exprimees separement bien qu'elles soient connectβes via une fonction d'echange. Les hypothèses d'ecoulement radial ainsi qu'une vitesse moyenne d'ecoulement furent faites. Les mouvements de convection resultants d'une difference de densites dûe aux variations de temperatures sont egalement consider°es. Le regime transitoire d'ecoulement de chaleur est evalue afin de determiner Ie flux de chaleur specifique. Ce resultat est ensuite integre dans l'èquation de transport afin d'evaluer les changements de concentration. Des solutions representant ce regime thermique transitoire, Ie transport des solutes ainsi que l'ecoulement permanent dans la masse rocheuse fracturee sont developpees. L'importance et l'influence du couplage thermique sur Ie transport des solutes sont discutees en detail. ZUSAMMENFASSUNG: In diesem Aufsatz wird ein mathematischer Ansatz vorgestellt, bei dem die unterschiedlichen Stoffkonzentrationen zwischen der Matrix und den Klueften durch eine Austauschfunktion gekoppelt werden. Der Ansatz liegt die Voraussetzung zugrunde, daβ die konvektive Fluidbewegung durch die Temperaturvariation hervorgerufen wird, die ihrerseits eine Funktion der Dichteunterschiede ist. Weiterhin, wird von einer radialen Konfiguration und eine mittlere Flieβgeschwindigkeit ausgegangen. Die Zeitabhangige Warmeleitung wird behandelt in bezug auf dem spezifischen Warmetransport. Konzentrationsanderungen werden durch Einbeziehung vom spezifischen Warmetransport in der Transportgleichung ermittelt. Die mathematische Beschreibung der instationaren und stationaren Warme- und Stofftransport im gekluefteten Gestein werden dargestellt und diskutiert. Es wird nachgewiesen, daβ sich die Einbeziehung von Warmetransport auf die Form und Art des Stofftransports auswirkt. 1. INTRODUCTION Solute transport through fractured rock masses has become a very important issue due to a recognized fact that the fate of a contaminant in a fractured medium can be significantly different from that in a homogeneous medium. Serious prediction errors may be made if this difference is neglected. In comparison with a fracture-dominated media or a homogeneous porous medium, pollutant migrations in a fractured porous medium may be attenuated due to molecular diffusion in the matrix. This, consequently, results in a rate reduction in the concentration change at each sampling location. This scenario is valid if the concentration in the fractures is greater than in the matrix. If this condition is reversed, solute tends to diffuse back into the fractures, which may cause additional pollutant spreading in the primary flow channels. As depicted in Figure 1, where с1 and с2 are the concentrations in secondary (matrix) and primary (fractures) flow pathways respectively, the contaminant is primarily transported through fractures when с1 = с2. However, the rate of transport in fractures begins to increase if the concentration in the fractures is less than that in the matrix, i.e. с2 < с2; this is matrix replenishment. Conversely, the rate of transport in the fractures starts to decrease if the concentration in the matrix is less than that in the fractures, i.e. с2 > с1; this is normal matrix diffusion. Figure 1 can be schematically represented by Figure 2, where the variable concentration changes in time actually replicate the abnormal breakthrough curves observed frequently in the experimental observations of breakthrough curves in solute transport through fractured porous media, as demonstrated by Figures 3 and 4.
ABSTRACT: This paper is mainly concerned with the influence of stress redistribution induced by excavation on the permeability change and groundwater flow around underground oil storage cavern. The exponential functions which describe the relationships of volumetric and lateral strains with permeability in elastic and plastic regions were derived and proposed. The deformational behavior of rock mass around cavern was analyzed using the finite element method, and the permeability change was evaluated by the relationships obtained from experimental results. The influence of permeability change on groundwater flow was also analyzed, and oil and gas leakage problems were investigated. RESUME: Cet article presente principalement I'influence de la redistribution des contraintes provoquees par I'exploitation sur Ie changement de permeabilite et ecoulement d'eau souterraine autour de la caverne pour stockage des petroles bruts. Les fonctions exponentielles que representent la relation de la deformation volumique et laterale avec la permeabilite dans les domaines elastiques et plastiques ont ete obtenues et proposees. Le comportement en deformation a ete etudie par la methode des elements finis, ainsi que Ie changement de permeabilite des massifs rocheux autour de la caverne a ete evalue par les relations obtenues des resultats experimentes. L'influence du changement de permeabilite sur l'ecoulement d'eau souterraine a ete analyse et les fuites de gaz et petroles sont egalement examinees. ZUSAMMENFASSUNG: Diese Untersuchung haldelt es sich urn den Einfluβ von der durch Abbruch hervorgerufenen Spannungsumlagerung auf Wasserdurchl assigkeits anderung und Grundwasserfluβ um einer untert agigen olspeicherkaverne. Die exponenten Funktionen sind abgeleitet und dargestellt, welche die Beziehungen von volumetrischer und lateraler Verformungen und Wasserdurchl assigkeit im elastischen und plastischen Bereich beschreiben. Das Verformungsverhalten der Felsmasse um Kaverne ist mit Finite-Elemente-Methode analysiert und die Permeabilit ats anderung ist mit der Versuchsergebnissen gewonnenen Beziehungen ausgewertet. Der Einfluβ der Permeabilittats anderung auf grundwasserfluβ ist analysiert und Sickerverlustprobleme von o1 und Gas sind untersucht, 1. INTRODUCTION Underground storage of crude oil and LPG has advantages of safety, environmental and economical aspects over above-ground storage systems and are very attractive commercially providing that geological conditions are favorable[l). The principles of oil and gas leakage control in underground oil storage cavern can be divided into permeability control and groundwater control. It, therefore, is very important to analyze the change of permeability of rock mass and groundwater level in designing grouting and water curtain system. This paper is mainly concerned with the influence of stress redistribution induced by excavation on permeability change and groundwater flow around underground oil storage cavern. The permeability around cavern is influenced by both blasting and stress relief[2](3). The influence of blasting on permeability change is confined to adjacent zone around cavern[3]. Therefore permeability change induced by stress redistribution was only considered. In this study, the relationship between strain and permeability was proposed based on a laboratory experiment using the transient pulse method[4]. The deformation behavior of rock mass around cavern was analyzed by the elasto-plastic finite element method and the changes of permeability was calculated using the relationship between strain and permeability. And an analysis of groundwater flow was carried out using the finite element method. The influence of permeability change on groundwater flow was analyzed and the oil and gas leakage was evaluated by considering the internal pressure of cavern. 2. SITE INVESTIGATION The underground oil storage facility is located at an island in southern Korea. It consists of six storage caverns, construction tunnels, connection tunnels and water curtain tunnels shown in Fig.1. The storage caverns are located at 30 ~ 60 m below a sea level and have a horse-shoe shaped cross section with a width of 18 m and a height of 30 m.