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Kirschner, David (Shell International Exploration and Production) | McAllister, Eddie (Shell Upstream Albania) | Davies, Christine (Shell Upstream Albania) | Campman, Xander (Shell Global Solutions International) | Duijndam, Bart (Shell Global Solutions International) | Li, Junlun (formerly with Shell International Exploration and Production) | Marquis, Guy (formerly with Shell International Exploration and Production)
ABSTRACT An integrated passive-source seismic and magnetotelluric study was executed in the Dinaride fold-thrust belt of central Albania in 2016. Ambient-noise surface waves originating from the North Atlantic and Mediterranean were recorded on a 380-node network that was deployed over a 500 km2 area for three months. Several hundred earthquakes were also recorded on the network. The data was analyzed by Sisprobe (Grenoble) to generate velocity cubes of the subsurface. Additional seismic data was recorded during a two-week deployment of 280 nodes along a 2D line. Magnetotelluric data was acquired at 105 sites and processed by Schlumberger (Milan) to generate a subsurface resistivity volume for two portions of the AOI. The results of these studies provide a three-dimensional image of the fold-thrust belt that helps explore the area. Presentation Date: Wednesday, October 17, 2018 Start Time: 1:50:00 PM Location: Poster Station 14 Presentation Type: Poster
Abstract Water injection has been used to increase oil recovery since the late 19 century. For over 100 years, the mechanisms behind this incremental oil recovery have been thought of as physical, i.e. the injection of water maintains reservoir pressure and sweeps the mobilised oil to the producing well. In the last decade this premise has been questioned and through the development of BP's LoSal™ EOR technology, it is now recognised that oil recovery through waterflooding also involves chemical processes and that modifying the brine chemistry of the injection water can significantly impact the observed recovery. Several hypotheses regarding the mechanism involved with low salinity waterflooding have been discussed in the literature. In 2006, BP published a proposed mechanism for this phenomenon based upon multicomponent ion exchange (MIE) triggered by expansion of the electric double layer at the mineral surfaces that bind the oil. This paper describes on going research studies focused on advancing the understanding of these mechanisms using sophisticated physical chemistry techniques such as Small Angle Scattering using neutrons from the ILL facility in Grenoble, France and the ISIS facility at the Rutherford Appleton laboratory, UK and X-rays at the DIAMOND Light source, Oxon. These techniques are capable of measuring the thickness of any water layer at the mineral surface down to the Angstrom level. Results to date provide some support for the BP published mechanism. They have shown the presence of a thin water layer and its variation with changes in the salinity of the water medium at model silica and clay-like surfaces, with attached (model) polar oil components, suspended in oils. Furthermore, the impact of cation-type on the water-layer thickness has also been demonstrated.
ABSTRACT The National Road RN 91 has been threatened for about twenty-five years by a huge landslide, located 25 km south-east to the town of Grenoble (France). If several million cubic meters of rock fall down, the debris will dam the valley. Then the failure of the dam by overtopping and rapid erosion might result in a catastrophic flood and dramatic consequences for human life, environment and economy throughout the valley. The paper presents the hazard assessment based on geological and hydrological surveys, including small scale hydraulic tests, as well as the risk evaluation that has been performed. The risk management relies first upon a high level monitoring and an emergency plan; various mitigation strategies have been considered. 1 INTRODUCTION In 1980, rock falls including blocks of limited size occurred on the National Road RN 91, in the valley of the Romanche river, approximately twenty kilometers southeast of Grenoble town (Figure 1). The starting point of the rocks, called "Les Ruines de Sechilienne", is located 300 m above the valley bottom, one kilometer downstream from Sechilienne village, in the French Alps. (Figure in full paper) Such rock falls are frequent in mountainous areas and nobody paid special attention to the event of 1980 as most of the slope was covered by a dense forest. But in 1985, new rock falls with large size blocks occurred and the road had to be closed during several days. An emergency monitoring was decided, during day and night. Soon afterwards a barrier of concrete blocks was set up along the road at the toe of the slope; the blocks were surmounted by detection wires connected to red lights located at both ends of the danger zone, one hundred meters long. The first geological surveys showed that the unstable area, not easily accessible and wooded, was not just a matter of one cliff generating some rock falls, but included a potential volume of a few million cubic metres. From the moment the landslide hazard was identified, the risk management was based on a monitoring system associated with an emergency plan. This system, initially composed of geodetic and extensometer manual measurements (cables stretched through fractures), was gradually developed and improved. In 1985–1986, as a first prevention measure, a diversion of the RN 91 was built in the valley floor, at the toe of the slope opposite to Les Ruines, with temporary bridges at each side of the exposed area. The heavy trucks had to keep using the old road. To avoid the potential wanderings of the river dammed by debris in case of a rockslide, a diversion channel has been dug; it is protected by an earth dyke, supposed to be able to retain 1–2 million m3 of debris. The final bridges for the road diversion were built a few years later. The main features of the hazard and risk evaluation linked to the moving rock mass are presented below.
Castelli, M. (Dipartimento di Ingegneria Strutturale e Geotecnica - Politecnico di Torino) | Allodi, A. (Dipartimento di Ingegneria Strutturale e Geotecnica - Politecnico di Torino) | Scavia, C. (Dipartimento di Ingegneria Strutturale e Geotecnica - Politecnico di Torino) | Frayssines, M. (Laboratoire Interdisciplinaire de Recherche Impliquant la Geologie et la Mecanique (LIRIGM) - Universite J. Fourier)
ABSTRACT: Aim of this paper is to show the role of rock bridges in the stability of fractured rock slopes through a Fracture Mechanics approach. To this purpose the numerical back analysis of the triggering phase of a 2000m3 rock fall occurred in Vercors (French Subalpine Ranges) in 2004 is carried out through the Displacement Discontinuity Method. The presence of rough and fresh surfaces on the detachment area after the failure induced to hypothesize the tensile propagation of natural discontinuities inside rock bridges. A detailed geological survey carried out on the detaching niche and the surrounding rock mass allowed the definition of a geometrical model while some laboratory tests carried out on the rock material allowed to obtain the mechanical parameters requested by the numerical method. On the basis of these data, some back analyses based on fracture mechanics allowed to simulate a toppling mechanism due to the tensile progressive failure of surveyed rock bridges. 1 INTRODUCTION The stability of fractured rock slopes is strongly related to the geometrical and mechanical characteristics of natural discontinuities, which require to be explicitly taken into account in the numerical analyses through a discontinuum approach. The model most widely used considers the discontinuities to be fully persistent, disregarding the presence of rock bridges inside the rock mass. However, this assumption can be highly pessimistic in terms of stability, because the presence of even small bridges of intact rock substantially increase joint strength (Einstein et al., 1983). Several models based on the Limit Equilibrium Method can be adopted to overcome this problem, referring to equivalent values of shear and tensile strength representative of the combined effect of joint surfaces and intact rock (Jennings, 1970; Einstein et al., 1983; Frayssines, 2005).However, this approach disregards the concentration of stresses at discontinuity tips, which gives rise to progressive failure in the structure. On the contrary, Fracture Mechanics makes it possible to take progressive failure phenomena into account through a study of the triggering and propagation of cracks starting from natural defects or discontinuities located in the rock mass. One of the earliest methods for the application of the principles of Fracture Mechanics to the assessment of the stability of rock structures was suggested by Tharp (1984). This method is based on the determination of the Stress Intensity Factors (SIFs) through expressions obtained from very simple geometry, neglecting the presence of a non-uniform state of stress in the slope. More recently the use of a numerical procedure, based on the BEM technique of the Displacement Discontinuity Method (DDM) (Crouch & Starfield, 1983), has been proposed by Scavia (1995) and Castelli (1998). 2 DESCRIPTION OF THE ROCK FALL AND DEFINITION OF THE GEOMETRICAL MODEL On January 30, 2004 a rock fall of about 2000m3 occurred in the Vercors Sub-alpine Chain, approximately 50 km south west of Grenoble (F). The rock mass came crashing down in the main road "D531", killing two people..
Foray, P.Y. (Laboratory 3S, Institut National Polytechnique de Grenoble, Grenoble, France) | Bonjean, D. (Laboratory 3S, Institut National Polytechnique de Grenoble, Grenoble, France) | Michallet, H. (LEGI (CNRS-INPG-UJF), Grenoble, France)
Coastal or offshore structures such as pipelines installed on the seabed are subject to cyclic horizontal loads either by direct hydrodynamic wave action or through the cyclic movement of risers or flow lines transmitted by floating structures. In fine sandy or silty soils, such cyclic loads may lead to liquefaction of the surrounding bed, which can play an important part in the processes of erosion, trenching or self-burial of the pipes. A large 1-g physical model was built to study the fluid-soil-structure interaction, with special emphasis placed on the conditions in which liquefaction occurs around a pipe instrumented with pore-pressure transducers. The experiments indicate a strong increase in pore pressure at the pipe-soil interface, and lateral visualization revealed the liquefaction of a soil band in the vicinity of the pipe. The penetration of the structure can be related to the phenomenon of liquefaction. INTRODUCTION The process of self-burial of structures resting on the seabed as a result of wave action has been extensively studied by Lyons (1973), Lambrakos (1985), Brennoden et al. (1986), Wagner et al. (1987), Palmer et al. (1988) and Morris et al. (1988), among others. Many of these studies were devoted to specific pipe-soil interaction in order to draw up design criteria for pipeline stability. The first experimental program was conducted at the University of Grenoble by Branque et al. (2001, 2002) to quantify the influence of cyclic amplitude and sand density on pipe penetration and changes in lateral resistance. Transitory liquefaction of the soil close to the pipe was noted in some of the tests, with peak cyclic pore pressures reaching the effective overburden stress. In recent years, increasing attention has been paid to the effect on the stability of coastal or offshore structures of wave-induced liquefaction, in combination with scour effects.
Foray, P.Y. (Laboratory 3S, Institut National Polytechnique de Grenoble) | Bonjean, D. (Laboratory 3S, Institut National Polytechnique de Grenoble) | Michallet, H. (LEGI, Institut National Polytechnique de Grenoble)
ABSTRACT Coastal or offshore structures such as pipelines installed on the seabed are submitted to cyclic horizontal loads either by the direct hydrodynamic wave action or through the cyclic movement of risers or flow lines transmitted by floating structures. In fine sandy or silty soils the cyclic loads can induce a liquefaction of the surrounding bed which can play an important part in the processes of erosion, trenching or self-burial of the pipes. A large 1g physical model was built to study the fluid-soil-structure interaction with special emphasis on the conditions of occurrence of liquefaction around a pipe instrumented with pore pressure sensors. The experiments indicate a strong increase in pore pressure at the pipe-soil interface and a lateral visualisation put into evidence the liquefaction of a soil band in the vicinity of the pipe. INTRODUCTION The process of self burial of structures resting on the seabed induced by the wave action has been extensively studied by Lyons (1973), Lambrakos (1985), Brennoden et al (1986), Wagner et al (1987), Palmer et al (1988), Morris et al (1988), among others. Many of these studies were devoted to the specific pipe-soil interaction in order to elaborate design criteria for pipeline stability. A first experimental program was conducted at the University of Grenoble by Branque et al (2002) to quantify the influence of the cyclic amplitude and the density of the sand on the penetration of the pipe and the evolution of the lateral resistance. A transitory liquefaction of the soil close to the pipe could be noted for some of the tests, with peak cyclic pore pressures reaching the effective overburden stress. In the recent years, an increasing attention has been given to the effect of wave-induced liquefaction on the stability of coastal or offshore structures, in combination with scour effects.
Allodi, A. (Politecnico di Torino - Dipartimento di Ingegneria Strutturale) | Castelli, M. (Politecnico di Torino - Dipartimento di Ingegneria Strutturale) | Marello, S. (Politecnico di Torino - Dipartimento di Ingegneria Strutturale) | Scavia, C. (Politecnico di Torino - Dipartimento di Ingegneria Strutturale)
ABSTRACT This paper investigates the possibility of interpreting the shear band evolution in hard soils and soft rocks as the result of shear propagation from pre-existing natural defects. This is done through the application of the principles of Fracture Mechanics, a Slip-Weakening Model (SWM) being used to simulate the non-linear zone at the tips of the discontinuity. Experimental observations have been carried out on prismatic samples of Beaucaire marl through biaxial compression tests in plane strain conditions. A numerical simulation confirms the validity of the proposed approach. RÉSUMÉ Cet article presente la possibilite d'interpreter l'evolution des bandes de cisaillement dans les roches tendres et les sols raides comme le resultat de la propagation pour cisaillement à partir d'un defaut preexistant. Le Slip-Weakening Model (SWM) a ete employe pour modeliser la zone non lineaire a l'extremite d'une discontinuite. Nous presentons des observations experimentaux obtenues à travers des essais de compression en deformation plane sur des echantillons prismatiques de marne. La simulation numerique d'un essai confirme la validite de la methode proposee. KURZFASSUNG Die vorliegende Arbeit versucht die Ausbreitung von Scherzonen in (bindigen) Böden und im Lockergestein anhand der Entwicklung von Scherrissen ausgehend von existierenden Schwachstellen zu erklaren. Die Umsetzung erfolgte mit Hilfe der Bruchmechanik, fuer die Modellierung der nichtlinearen Zone an den Rissenden wurde ein Slip-Weakening-Modell (SWM) eingesetzt. Es wurden zweiaxiale Druckversuche an prismatischen Probekörpern von Beaucaire Mergel unter der Bedingung eines ebenen Verzerrungszustandes durchgefuehrt. Die numerische Untersuchungen bestatigten die Annahmen der untersuchten Theorie. Introduction Several observations in laboratory compressive tests indicate that somewhere near the peak load, rock deformation becomes localized and, after the peak, evolves into a fracture, fault, shear band, rupture zone or simply a failure plane (Waversik & Fairhust, 1970; Labuz et al., 1996). Complete and accurate experimental results are given by a series of tests carried out at the Laboratory 3S in Grenoble. For such tests a biaxial apparatus, developed by Desrues (1984) and modified by Charrier et al. (2001), has been employed in plane strain conditions. The results of the tests, carried out in undrained conditions and without stress confinement, has been elaborated by means of a stereo-photogrammetric technique (Desrues, 1984, 1995). Such analysis allows to obtain a complete and quantitative representation of the specimen deformation and explicit data relative to the formation and propagation of shear bands. Microscopical studies based on Fracture Mechanics (Reches & Lockner, 1994; Horii & Nemat-Nasser, 1985), show that a shear fault nucleates by local interaction among a few micro-cracks and that it propagates into the unfaulted region by inducing micro-crack growth at its front. This micro-structural process of breakdown near the crack tip can be interpreted by assuming that it gives rise to cohesive stresses, which oppose the action of applied loads. Thus, a Non Linear Fracture Mechanics approach, based on a cohesive-zone model, seems promising for an appropriate macroscopical representation of shear crack propagation in rock. Palmer & Rice (1973) first developed such model (Slip-Weakening Model, SWM, also analyzed by Li, 1987).
ABSTRACT: The Sechilienne slope movement has been extensively monitored for 10 years. The moving volume is estimated to 100 hm and possible partial ruptures could destroy houses and dam the valley. The main features of the movement are opening of vertical fractures, slightly dipping displacements and no sign suggesting an outcropping sliding surface. A 2D geomechanical model was elaborated and the distinct element method used to investigate the slope deformation mechanism. A deep seated deformation mode, with simultaneous sliding and toppling of blocks, is proposed to explain the field observations and measurements. RESUME: Le mouvement de versant de Sechilienne est l'objet d'une auscultation et d'une surveillance intensives depuis une dizaine d'annees. Le volume en mouvement est estime à 100 hm et de possibles ruptures partielles pourraient provoquer la destruction de plusieurs habitations et barrer la vallee, Les principales caracteristiques du mouvement sont l'ouverture de fractures verticales, la faible inclinaison des deplacements et l'absence d'indices suggerant I'existenced'une surfacede glissement affleurante, Un modele geomecanique bidimensionnel a ete elabore et la methode des elements distincts a ete utilisee pour rechercher Ie mecanisme de deformation du versant. Un mode de deformation profond, avec glissement et basculement simultane s de blocs. est propose pour expliquer les observations et mesures de terrain. ZUSAMMENFASSUNG: Die Hangbewegungen von Sechilienne sind seit etwa 10 Jahren im Brennpunkt von Beobachtungen und genauester Ueberwachung. Das Gesamtvolumen in Bewegung wird auf 100 h,3 geschaetzt, Moegliche Teilfraktionen koennten die Zerstoenmg von mehreren Behausungen und ein Aufstauen des Tales bewirken. Die wichtigsten Charakteristika des Vorganges sind vertikale Frakturoeffuungen, schwach ausgepraegte Fliessbewegung und Abwesenheit von Indizien, die auf eine oberflaechliche Gleitbewegung hindeuten koennten. Ein zweidimensionales geomechanisches Modell wurde. entwickelt und die Methode der unterschiedlichen Elemente wurde angewandt, um den Mechanismus der Hangbewegung zu erforschen. Ein tiefreichender Deformationsmodus inklusive simultaner Rutsch- und Stossbewegungen von Felsbloecken wird als Erklaerung der Beobachtungen und Messungen vor Ort vorgeschlagen. EXTENDED SUMMARY Introduction Rock slope failures are source of major risks in mountainous regions. Anisotropic. metamorphic rocks show all kinds of failure mechanisms., The case of the Sechilienne movement is of great interest due to the complexity of its deformation mechanism, revealed by an extensive monitoring during the decade 1988–98. The movement is located on the southfacing flank of the Romanche valley, 20 km upstream from Grenoble. Its reactivation in 1985 proved dangerous for a major highway and led to, a complete geological survey of the slope and to the installation of a large monitoring net to measure surface displacements. The unstable volume proved bigger than initially expected, implying possible destruction of houses and damming of the valley. Consequently, the monitoring device was complemented by a 240 m long gallery. Finally, the unstable volume was estimated to 100 hm3. Description of the slope and the movement The slope angle is approximately 40° in the lower part (altitude: 330 m to 950 m) and 20° in the upper part (950 m to the top of the mountain at 1125 m), Near the crest, a 20 m high cliff reveals an old settlement (figure 1).
ABSTRACT: Near Grenoble (French Alps), a 100 million cubic meters slope movement threatens the Romanche valley and has been monitored since 1985. The deformation mechanisms are very difficult to identity. A simplified geomechanical model of the rock mass has been used to simulate the excavation of the valley, with finite and distinct element methods. The results obtained allow to explain some morphological features of the slope and are compatible with the present movements. RESUME: Pres de Grenoble (Alpes françaises), un mouvement de versant de 100 millions de mètres cube, qui menace la vallee de la Romanche, est ausculte depuis 1985. Les mecanismes de deformation sont très difficiles a identifier. Un modèle geomecanique simplifie du massif rocheux a ete utilise pour simuler I'excavation de la vallee, par les methodes des elements finis et des elements distincts. Les resultats obtenus fournissent une explication de certains traits morphologiques du versant et sont compatibles avec les mouvements actuels. ZUSAMMENFASSUNG: Nahe Grenoble (französische Alpen) befindet sich ein seit 1985 unter Beobachtung stehendes Hangrutschungsgebiet mit einem Volumen von 100 Millionen Kubikmetern, welches das Tal der Romanche bedroht. Die Verformungsmechanismen sind sehr schwer identifizierbar. Ein vereinfachtes geomechanisches Modell der Felsböschung mit finiten und distinkten Elementen wurde zur Simulation der Talentstehung genutzt. Die erhaltenen Ergebnisse erklaren einige morphologische Besonderheiten dieser Felsböschung und entsprechen den momentan stattfindenden Bewegungen. 1 INTRODUCTION Deformation mechanisms of some large slope movements in mountain areas are very difficult to identity. To be understood, they need to be considered as the result of a long term geological process, and then to be analyzed in the appropriate space-time scale. This is the case for the Sechilienne slope movement, which will be described later. The geomechanical models presented in this paper have been elaborated to highlight the evolution of the rock mass, due to the formation of the valley, and to analyze the influence of different factors on its present behaviour. The models are not aimed at predicting the future behavior of the slope. We think that, for movements which are as complex as the Sechilienne landslide, geomechanical simulations are not sufficient for this purpose, and must be used together with more empirical approaches. 2 DESCRIPTION OF THE SECHILIENNE SLOPE MOVEMENT The Sechilienne slope movement takes place on the north flank of the Romanche valley, 20 km upstream from Grenoble (Figure 1). Rockfalls at the front of the unstable mass were well known by the former generations of inhabitants who called the site "Les Ruines" Their reactivation in 1985 proved dangerous for a major highway (RN 91) and led to a complete geological survey of the slope and to the installation of a large monitoring net to measure displacements, by geodesy and extensometry. These studies showed that the movement extends up to the crest and, consequently, that the unstable mass is much larger than the 3 million cubic meters of the very active frontal zone. First volume estimation of the unstable mass was 50 million cubic meters but recent geodesic and underground observations lead to an estimation of about 100 million cubic meters. Different rockfall scenarios have been studied to estimate and prevent the damages wind effect, damming of the valley, flooding …
ABSTRACT: Numerical modelling of rock cutting process at great depth is discussed in this paper. The failure of rock is assumed to be formed and developed through shear band strain localization. For detecting its onset, two localization indicators, the bifurcation criterion and a scalar indicator, were used. As classical finite elements cannot always give us a reliable result because of the very high strain gradient produced across the thin band thickness, the spectral band superposition technique proposed initially by Belytschko is discussed in the large strain framework. The numerical results of the rock cutting are given to show the availability of above theoretical and numerical tools. RESUME: On discute dans cet article la simulation numerique de la coupe de roche à grande profondeur. La rupture de roche s'interprète par la localisation en bandes de cisaillement. Pour l'indiquer, deux critères, Ie critère de bifurcation et un indicateur scalaire, sont utilises. Comme les elements finis classiques perdent souvent efficacite face aux problème de localisation, la technique de superposition des bandes spectrales proposee initialement par BELYTCHKO est discutee dans un contexte de grandes deformations. Les resultats numeriques de la coupe de roche montrent l'efficacite de l'ensemble des developpements theoriques et numeriques. ZUSAMMENFASSUNG: Dieser Artikel behandelt die nwnerische Simulation des Felsschneidvorgangs in groβer Tiefe. Es wird angenommen, daβ der Felsbruch durch die Entwicklung von Scherverformungsstreifen ensteht. Um deren Auftreten anzuzeigen wurden zwei Kriterien verwendet: ein Verzweigungskriterium und ein skalarer Rechenfaktor. Da klassische finite Elemente die damit verbundenen, lokal sehr hohen Verformunsgradienten oft nur in unbefriedigender Weise darstellen können, wird eine, eingangs von BELYTSCHKO vorgeschlagene, spektrale ueberlagerungsmethode im Zusammenhang mit groβen Verformungen vorgestellt. Numerische Ergebnisse zum Felsschneidvorgang untermalen die wirksamkeit dieser theorischen und numerischen Entwicklungen. 1. INTRODUCTION Numerical modelling of the rock cutting process in petroleum engineering will help us to understand rock behaviour and to improve cutting efficiency and to design a new cutter. There are two main challenges for this modelling. The first one is to indicate the onset of this failure precisely, i.e. when and where it appears and how it develops. The second one is to simulate the complete process up to the failure state and the excavation of chips. It is assumed that the failure of rock is formed-and developed through shear band localization. The bifurcation criterion  is used to judge the beginning, the development and the nature of a slip or a rupture. It is generally- very efficient, but for some geotechnical applications, the indicated localized region may be very widespread and so the potential band definition remains vague and imprecise. For this reason, a scalar indicator is proposed. As the classical finite element method cannot always give a reliable result because of the very high strain gradient produced across the thin band thickness, the spectral band superposition technique, proposed initially by Belytschko [2–4], is used. It consists in using the spectral interpolation in conjunction with a finite element one to enhance the accuracy of the numerical approximation for the problems with high velocity gradient. The problem to be solved is idealized in Fig. 1. A single cutter is pressed against a piece of rock located at a great depth (about 2500 m). Plane strain state condition is supposed. Mud pressure is imposed as the boundary condition. A coarse discretization is realised using about 170 isoparametric 8-node elements. The hypoplastic law CLoE, developed at the laboratory 3S of Grenoble, is used for describing the rock constitutive behaviour.