Cette étude expérimentale traite la localisation des déformations sur un grès poreux: le grès de Vosges. Un nombre des essais triaxiaux sont effectués sous des pressions de confinement (i.e., 20 MPa - 190 MPa) et des déformations axiales différentes pour mieux comprendre la réponse mécanique de ce grès. La localisation des déformations a été étudiée dans des différentes échelles en appliquant une variation de mesures de champs (full-field methods) comme la Tomographie Ultrasonore (en 2D), les Emissions Acoustiques (en 3D), les Rayons X (en 3D), et la Corrélation des Images (en 3D). Les méthodes expérimentales ont été appliquées avant, pendant et après les essais triaxiaux. Des coupes fine ont été observées sous le microscope optique et électronique (SEM). La combinaison des multiples techniques expérimentales, qui ont des différentes sensitivités et résolutions, a décrit la procédure de la formation et l’évolution des bands de déformation observées sur le grès de Vosges. Des bandes de cisaillement ont été formées sous des pressions intermédiaires et des bandes de compaction sous des pressions élevées. Des bandes de compactions pure n’ont pas été observées.Les bandes de déformations observées se sont caractérisées comme des zones de déformation de cisaillement localisée et/ou de compaction. En plus, elles se sont caractérisées comme des structures de fable vitesse ultrasonore, des places d’origine des fissures inter- ou intra- granulaires, et des places des densités de matériel élevées.Deux mécanismes principales ont été observées au niveau de grain dans les bandes de cisaillement et de bandes de compaction (shear-enhanced compaction bands): d’un cote c’est la fissuration des grains (endommagement) et de l’autre cote c’est la réduction de porosité (sur la forme de compaction). Les deux mécanismes i présent différences sur leurs proportions et leur ordre d’occurrence dans le temps. / This PhD thesis presents a laboratory study aiming at a better understanding of the stress-strain response of the Vosges sandstone (porous rock) tested at a range of confining pressures (i.e., 20-190 MPa) and different axial strain levels. Localised deformation was captured at different scales by a combination of full-field experimental methods, including Ultrasonic Tomography (2D), Acoustic Emissions (3D), X-ray Tomography (3D), and 3D volumetric Digital Image Correlation, plus thin section and Scanning Electron Microscope observations (2D). These experimental methods were performed before, during and after a number of triaxial compression tests. The combined use of the experimental techniques, which have different sensitivity and resolution, described the processes of shear band and shear-enhanced compaction band generation, which formed at low to intermediate and relatively high confining pressures, respectively. Pure compaction bands were not identified. The deformation bands were characterised as zones of localised shear and/or volumetric strain and were captured by the experimental methods as features of low ultrasonic velocities, places of inter- and intra-granular cracking and structures of higher density material. The two main grain-scale mechanisms: grain breakage (damage) and porosity reduction (compaction) were identified in both shear band and shear-enhanced compaction band formation, which presented differences in the proportions of the mechanism and their order of occurrence in time.

Granular materials are characterized by its discrete nature which makes their behaviour very complex to understand when subjected to various loading situations. Comparing other materials, the understanding of granular materials is poor. This is because experimental analysis provides the macroscopic responses of the considered assembly whereas the discrete nature of the particles point to the fact of understanding the micro scale details and correlating it with the overall behaviour. Among the various modeling tools viz. analytical, physical or numerical, Discrete Element Method (DEM) a numerical technique, originally developed by Cundall (1971, 1974) and modified by Cundall and Strack (1979a, 1979b) is widely used for granular materials. Later a thorough description of DEM was given by Cundall (1988) and Hart et al (1988). Moreover Cundall & Hart (1992) reported discrete element code as one which allows finite displacements and rotations of discrete bodies along with recognition of new contacts as the calculation progresses which is followed in particle flow code and is used for this study. Generally the discrete particles are modeled as discs or spheres in 2-D and 3-D simulations respectively. The discs or spheres were considered as it is very easy to characterize the grain interactions and the contact detection. Even though the significance of particle shape has been reported in literature, a comprehensive 3-D study of the effect of particle shape on the various aspects of soil behaviour is lacking and is not reported. Particle shape is generally defined in terms of elongation, roundness and texture. Elongation is an indication of the particle aspect ratio whereas roundness measures the sharpness or angularity of particle’s edges and corners. Texture is related to the roughness of the surface. Particle gradation also plays a role in the mechanical behaviour. The influence of each of these factors on the mechanical behaviour of the assembly is important. Hence the major factors like elongation, texture etc which are used to define the particle shape are incorporated in this study. Evaluating the particle shape is another hurdle. In this study, the particle shape is analyzed using a 3D laser scanner which helps to identify the major and minor axis lengths of the particle. Additionally, the effective use of 3D DEM on large scale real life applications incorporating the particle shape effect is also not dealt with very extensively. Hence in this research, a comprehensive study on the calibration of DEM using glass beads, effect of particle shape on drained and undrained monotonic behaviour, liquefaction, post liquefaction and dynamic properties and the application of DEM to a grain polishing machine and an underground tunnel assembly is presented. In the present study, a set of drained triaxial tests were done on glass bead assembly using a laboratory triaxial set up. The glass beads used for the test were spherical and ellipsoidal in shape. The shape of glass beads was characterized through a sophisticated method of 3D laser scanning. In this scanning, the shape of the image of the glass bead is captured through an array of digitized points. These images obtained as unstructured 3D triangular meshes on processing will render the long and short axes of the particle which can be used for proper modeling of the particle shape. After obtaining the long and short axes for the particles, the same is used for the numerical modeling of the glass beads. The numerical simulation results have shown that the assembly modeled with clumped particles gives results qualitatively and quantitatively similar to the observed experimental macro responses. Hence this is used to demonstrate the power of DEM to realistically model the granular behaviour by incorporating the particle shape effect. In addition, undrained simulation of granular material has been numerically predicted from drained triaxial tests which are similar to the approach proposed by Norris et al (1997). An excellent correlation between undrained results predicted from drained triaxial test and undrained test (performed under constant volume conditions) has been observed. This further underlines the fact that the constant volume simulations are equivalent to undrained tests. Having validated the DEM results to the values obtained from the experiments on glass beads, a series of monotonic drained and undrained triaxial tests were performed on cylindrical assemblies of height to diameter ratio 2:1. Four different sets of assemblies were prepared which consists of particles of different aspect ratio to study the influence of particle shape. The behaviour of these assemblies under drained shearing indicates that the strength of the clumped assemblies is higher than that of the spherical assembly at all confining pressures. This has been explained from the magnitude of the anisotropic vi coefficients associated with the fabric and normal contact force tensors. It is also noted that eventhough both assemblies reach the peak strength at the same axial strain, the strain softening associated with the clumped assembly is very rapid which is due to the fact that clumps try to push each other apart as it offers more resistance to rotation resulting in dilation. Another significant observation is that a general increase in aspect ratio will not keep on increasing the strength. As the aspect ratio increases, the particles have a tendency to orient along their larger dimensions. This helps them to attain the lowest potential energy leading to a stable equilibrium and resulting in inherent fabric anisotropy. But when the particles try to align along the larger dimension, the formation of strong contact forces along the direction of loading is hindered. In addition, the lower strength associated with the higher aspect ratio particle assembly can also be attributed to the formation of unexpected void spaces when these longer particles bridge gaps over the underlying grains. The critical state studies indicate that the clumped assembly is having a higher residual strength compared to that of the spherical assembly. In the case of clumped assemblies also, irrespective of the initial loose or dense state of the assembly and the confining pressure applied, the samples reached the same critical state which underlines that the critical state is unique for a granular material. Moreover, the critical state line is non-linear for both the spherical and clumped assemblies. The studies conducted on the liquefaction behaviour indicates that at lower confining pressures the assemblies with particles consisting of lower aspect ratios loses its strength at less number of cycles which can be attributed to the interlocking of non-spherical particles resulting in higher number of contacts per particle. Moreover, during the initial cycles of loading, it is seen that the strong contacts are predominantly in the vertical direction or more precisely along the direction of maximum axial strain. But the plots extracted at higher cycles indicated that the strong contacts along the vertical direction have diminished considerably. This reduction in contact force magnitude and force chain indicates a drop in the number of contacts and is clearly visible in the gradual decrease of average coordination number. Another significant observation is that as the confining stresses increases, the rate of pore pressure generation of the assembly vii consisting of only spherical particles is less compared to the other two samples. Furthermore, at higher confining pressures, when the load direction reverses, the fabric of the clumped assemblies fails to change to a new orientation immediately. But to retain equilibrium the force anisotropy will quickly adjust itself. This mismatch results in losing the contacts and resulting in lower strength and less resistance to liquefaction at higher stresses for assemblies consisting of clumped particles. The post liquefaction study of the numerically liquefied samples shows that the assembly consisting of clumped shaped particles gained strength at a much faster rate compared to the assembly consisting of only spheres. This may be attributed to the ability of the clumps to rearrange themselves on a faster rate compared to that of the spherical particles. The rate of development of average coordination number is very significant as it explains the ability of the assembly to build up the deviatoric stress from a complete collapsed structure. As the contacts develop, the average coordination number as well as the deviatoric stress starts increasing with both the values higher for the assembly consisting of clumped particles. The evaluation of the dynamic properties viz. shear modulus and damping ratio showed a trend similar to the experimental observations on real granular materials. It is observed that the normalized shear modulus reduces with an increase in shear strain and the rate of reduction is very high at low strains for all the samples. It can be seen that as the confining pressure increases, the normalized shear modulus value also increases and the rate of increment is higher for the assemblies consisting of non-spherical particles. Furthermore, for all the samples the threshold shear strain is about 0.001 up to which the behaviour is elastic. Beyond the threshold shear strain, the variation of the normalized shear modulus ratio is non-linear. At small shear strains, the energy dissipation is low resulting in smaller values of damping. As the strains increase, the non-linearity in the constitutive behaviour results in higher material damping leading to high damping value. The simulations of the food polishing machine helps to understand the pattern of hitting of clumped grains on the wall with due importance to the velocity of hit, angle of hit, force of hit, and the number of grains hitting the wall. The modeling and subsequent extraction of the data helped to identify that the wear and tear of the machine was not uniform and was clustered to specific regions due to the non-uniform distribution of the considered parameters. This helped to design a more sophisticated system such that the parts which are subjected to more deterioration are provided with additional support. To bring out the effect of the particle shape, simulations are performed using spherical particles and the results show that the pattern of variation is same, but the magnitudes are different owing to the less surface area associated with the spherical particles. The 3-D simulations of an underground tunnel assembly in a weak weathered rock helped to understand the variation in the stability of the system with and without lining. It was observed that the introduction of lining resulted in a more stable configuration and the circumferential stresses were found to be distributed uniformly around the tunnel. FEM simulations also show a similar trend of stress and strain variations but were unable to capture the ground loosening around the tunnel and the formation of the ground arch whereas DEM could realistically capture all these phenomena. It was observed that as the shape changes from sphere to non-spherical particles, circumferential stresses around the tunnels increased. In addition, as the distance from the tunnel face increases, the strains are reduced. The maximum vertical strain near the crown of the tunnel is observed for the assembly consisting of spherical particles. In short, this research is focused on a comprehensive understanding of the particle shape effect on the mechanical behaviour of granular mass. Numerical simulations incorporating the shape effect has been done on drained and undrained monotonic shear tests, critical state, liquefaction, post liquefaction and dynamic properties. Besides, the granular dynamics simulation of the movement of long food grains in a food polishing machine and the behaviour of an underground tunnel in a granular assembly is also reported.

[pt] As reservas de óleos pesados têm obtido grande importância devido à diminuição das reservas de óleos leves e ao aumento dos preços do petróleo. Porém, precisa-se de aumentar a viscosidades destes óleos pesados para que possam fluir até superfície. Para reduzir a viscosidade foi escolhida a técnica de recuperação térmica SAGD (Steam Assisted Gravity Drainage) pelos seus altos valores de recobro. A redução da viscosidade é atingida pela transmissão de calor ao óleo pela injeção de vapor, porém uma parte deste calor é transmitida à rocha. Esta transmissão de calor junto com a produção de óleo geram uma variação no estado de tensões no reservatório o que por sua vez geram fenômenos geomecânicos. Os simuladores convencionais avaliam de uma forma muito simplificada estes fenômenos geomecânicos, o que faz necessários uma abordagem mais apropriada que acople o escoamento dos hidrocarbonetos e a transmissão de calor com a deformação da rocha. As mudanças no reservatório, especialmente a variação da saturação, afetam as propriedades sísmicas da rocha, as quais podem ser monitoradas para acompanhar o avanço da frente de vapor. A simulação fluxo-térmica-composicional-geomecânica é integrada à sísmica de monitoramento 4D da injeção de vapor (a través da física de rochas). Existe uma grande base de dados, integrada por propriedades dos fluidos do reservatório (PVT) (usado no arquivo de entrada de simulação de fluxo) e uma campanha de mecânica das rochas. Foram simulados vários cenários geomecânicos considerando a plasticidade e variação da permeabilidade. Foram avaliadas várias repostas geomecânicas e de propriedades de fluidos no pico de pressão e final do processo SAGD. A resposta geomecânica pode ser observada, porém foi minimizada devido à baixa pressão de injeção, sendo o mecanismo de transmissão de calor um fator importante na produção de óleo (pela redução da viscosidade) e a separação vertical entre poços. Foi também significativa à contribuição da plasticidade no aumento da produção de hidrocarbonetos. A impedância acústica foi calculada usando a Equação de substituição de fluidos de Gassmann. Os sismogramas sintéticos de incidência normal (para monitorar o avanço da frente o câmara de vapor) mostraram a área afetada pela injeção de vapor, porém com pouca variação devida principalmente à rigidez da rocha. / [en] The heavy oil reserves have gained importance due to the decreasing of the present light oil reserves. Although it is necessary to reduce the oil viscosity and makes it flows to surface. For its high recovery factor the SAGD (Steam Assited Gravity Drainage) thermal process was selected. The viscosity reduction is achieved by heat transfer from steam to oil, but some part of this heat goes to rock frame. This heat transfer together with oil production change the initial in-situ stress field what creates geomechanical effects. The conventional flux simulators have a very simplified approach of geomechanical effects, so it is necessary to consider a more suitable approach that considers the coupling between oil flux and heat transfer with rock deformation. The changes within the reservoir, specially the saturation change, affect the seismical rock properties which can be used to monitor the steam chamber growth. The flux-thermal geomechanics is integrated to steam chamber monitoring 4D seismic (through the rock physics). There is a great data base, integrated by reservoir fluid properties (PVT) (used in reservoir simulation dataset) and a rock mechanics campaign. Several scenaries were simulated considering the plasticity and permeability variation. Several geomechanical responses and flux properties at peak pressure and end of SAGD process were evaluated. The geomechanical response can be observed, but was minimized due to low steam injection pressure, being the heat transfer an important in oil production (for the viscosity reduction) and the vertical well separation, too. The plasticity has a significant contribution in the increment of oil production. Acoustic impedance was calculated by using Gassmann fluid substitution approach. 2D Synthetic seismograms, normal incidence (to monitor the steam camera front advance), showed the area affected by steam injection, but with little variation due principally to rock stiffness.

The aim of the EU BIOMOre Project is to investigate the potential to extract copper from Sandstone formations in the North-Sudetic Trough which lies along the border between Poland and Germany. A new mining concept called bioleaching shall be applied in thin and very low permeable copper mineralization zones (order of 0.2 mD). Briefly, bioleaching process is the injection of a lixiviant (sulphur acid containing ferric iron) and then extraction of a pregnant leach solution through boreholes at the ground surface. This concept requires another special technique which is called hydraulic stimulation. Cracks along a wellbore are generated by pumping large quantity of fluid under high pressure into a cased section of rock during a hydraulic stimulation. This work at hand focuses on the geotechnical methods and scientific-engineering approaches used for extracting copper from very thin mineralization zones. The geological setting with faults and in situ stress state of the exploration zone is generated using measurements, visualised by 3D CAD model (RHINO), and computed via the Discrete Element code 3DEC. The preliminary drilling (stacked dual lateral wellbore) and stimulation design (plug-and-perf completion) are selected based on comprehensive literature survey and industry-based consultancy. In order to calibrate the calculated stress state in 3D, candidate sites for the hypothetical drilling-stimulation are detected using 2D GIS map (QGIS) at CAD model (RHINO). Trend of calculated stresses is in good agreement with the measured ones (σH > σv > σh). The final decision of selecting a drilling-stimulation site is made by using both GIS map and 3D CAD model. A hypothetical drilling-stimulation can be performed up to the depth of 1564 m in the Rotliegend & Grauliegend Sandstone with shale, which is overlain by (Zechstein) Limestone. During a possible stimulation, limestone’s integrity as a caprock and as a stress barrier is of great importance in addition to connect two lateral wellbores for facilitating flow of lixiviant. The preliminary geometrical design of stimulation is set with the cluster spacing (distance between fractures) of 20 m. Subsequent to final cost estimation of selected preliminary drilling-stimulation design, it is decided to use pinpoint (1,200,000 Euro) instead of plug-and-perf completion (2,345,300 Euro) since it is more economical. A possible drilling operation is anticipated to cost approximately 9,000,000 Euro. The 3D in situ stress model is calibrated before transferring of stress state into the sub-model which is used to optimise the selected stimulation design. The results of the last (DEM) sub-model are employed to reduce costs, to enhance the connection between branches of wellbores for bioleaching and to hinder possible penetration of fractures into the caprock. The preliminary geometrical design of stimulation is then modified based on these calculation results while increasing the cluster spacing from 20 m to 40 m. This is performed due to high stress-shadows (alteration of the stresses between fractures in a stimulation) encountered at the preliminary calculations. Results showed that, after the 80 seconds injection duration of water with 0.16 m3/sec into the sandstone, two wellbore laterals are expected to be connected by three generated cracks. They exhibit average aperture and transmissivity of 4.1 mm and 5.8 . 10-8 m2/sec, respectively. Furthermore, fracture initiation pressure ranges between 30 – 35 MPa at the drilling depth. The conclusions can be drawn that through the assessment of 3D CAD, GIS, and numerical DEM modelling methods, approximately 49% of cost reduction can be achieved by employing pinpoint instead of plug-and-perf completion. That is an important proof of the systematically approach for a stimulation planning wherein all necessary phases such as in situ stress estimation, modelling and cost assessment should have been considered. This work can be considered as a milestone for studies of stimulation designs which has been newly initiated in the EU-Region as a promising method for efficiency considering unconventional ore extraction. Moreover, this dissertation revealed again the emerging importance of integrated geotechnical information systems analogous to BIM (Building Information Systems).:LIST OF FIGURES LIST OF TABLES NOMENCLATURE ABSTRACT ZUSAMMENFASSUNG ACKNOWLEDGEMENTS 1. OUTLINE AND OBJECTIVE OF THE DISSERTATION 2. STATE OF THE ART 2.1. INTRODUCTION TO STIMULATION TECHNOLOGIES, EQUIPMENT AND DESIGNS 2.1.1. Technical instruments and frac-materials 2.1.2. Wellbore completion designs 2.1.3. Location and orientation of a wellbore 2.1.4. Fracture placement designs 2.1.5. Summary and conclusions 2.2. MEASUREMENT AND MODELLING OF UNDERGROUND STRESS FIELD 3. DETERMINATION AND MODELLING OF IN SITU STRESS FIELD IN THE NORTH SUDETIC TROUGH 3.1. GEOLOGICAL SETTING OF THE MODELLED REGION 3.2. SIMULATION OF THE IN SITU STRESS FIELD 3.2.1. Determination of the stress regime by measurements 3.2.2. Stepwise procedure of the stress field modelling 3D CAD assisted structural model of geological setting 3D DEM model for stress field simulations 2D GIS maps used for detection of drilling-stimulation sites 4. DRILLING AND WELLBORE DESIGN CALCULATIONS WITH COST ESTIMATION 4.1. DESIGN CALCULATIONS AND TECHNICAL REQUIREMENTS OF DRILLING AND WELLBORE 4.2. ECONOMICAL EVALUATION OF THE SELECTED DRILLING AND WELLBORE DESIGN 5. MODELLING OF THE HYDRAULIC STIMULATION AT THE SELECTED DRILLING SITE IN SANDSTONE 5.1. FINAL CALIBRATION OF THE 3D STRESS FIELD MODELS 5.2. DISCRETE ELEMENT MODELLING OF THE STIMULATION DESIGN AT THE SELECTED DRILLING SITE 5.3. DESIGN OPTIMIZATION STUDY OF THE STIMULATION MODEL AND FINAL COST ESTIMATION 6. SUMMARY AND CONCLUSIONS REFERENCES APPENDIX-A APPENDIX-B APPENDIX-C