Zugl.: Berlin, Techn. Univ., Diss., 2009

Unsicherheiten bei der Exploration von Kohlenwasserstoffreservoiren kann mit einer Teilkopplung von geologischen, geomechanischen und bruchmechanischen Modellen begegnet werden. Durch ein Simulations-Kopplungs-Interface kann etablierte Software herstellerübergreifend genutzt werden, ohne dass zusätzliche Erweiterungen seitens der Hersteller notwendig sind. Bei dieser Kopplung auftretende Maßstabseffekte werden mit zwei eigens entwickelten Triaxialgeräten zur Untersuchung der geomanisch-hydraulischen Zusammenhängen von Festgesteinen betrachtet.

The anisotropic behavior of a rock mass with persistent and planar joint sets is mainly governed by the geometrical and mechanical characteristics of the joints. The aim of the study is to develop a continuum-based approach for simulation of multi jointed geomaterials. There are two available numerical techniques for the strain-stress analysis of rock masses: continuum-based methods and discontinuum based methods. Joints are simulated explicitly in discontinuous methodology. This technique provides a more accurate description for the behavior of a rock mass. However, in some projects, the explicit definition becomes impractical, especially with increasing number of joints. Besides, the calculation efficiency will be significant reduced as the number of joints increases within the model. Considering the above mentioned shortcomings of the discontinuous method, the continuum-based approach is widely used in rock mechanics. Within the continuum methods, the discontinuities are regarded as smeared cracks in an implicit manner and all the joint parameters are incorporated into the equivalent constitutive equations. A new equivalent continuum model, called multi-joint model, is developed for jointed rock masses which may contain up to three arbitrary persistent joint sets. The Mohr-Coulomb yield criterion is used to check failure of the intact rock and the joints. The proposed model has solved the issue of multiple plasticity surfaces involved in this approach combined with multiple failure mechanisms. The multi-joint model is implemented into FLAC and is verified against the distinct element method (UDEC), analytical solutions, and experimental data. Uniaxial compression tests with artificial rock-like material (gypsum) are carried out in the laboratory in order to verify the developed constitutive model and to investigate the behavior of jointed specimen. Samples with two crossing joints covering more than 20 angle configurations and two different property sets were prepared and tested. Simulation results are in good agreement with experimental observations. The developed model is applied to two potential practical applications: the stability analysis of a slope and a tunnel under different stress conditions. Finally, the main achievements of the whole PhD study are summarized and future research work is proposed.

Im Projekt GeoStab wurde eine numerische Methode entwickelt zur integralen Bewertung der Gebirgsstabilität des Untergrundes auf der Grundlage regionalgeologischer 3D-Modelle. Dabei wurden natürliche Objekte – wie Störungszonen sowie Gebirgsbereiche um unterirdische Hohlräume (z.B. Altbergbau oder Tunnel) – besonders berücksichtigt. Mit der entwickelten Methode können beschrieben werden Deformationen an Diskontinuitäten, großräumige Spannungs- und Deformationsfelder des Untergrundes und der Einfluss bergbaulicher Grubenfelder auf die Stabilität des umgebenden Gebirges. Die Methode soll Behörden dazu dienen, bei Infrastrukturprojekten wie Tunnel- oder Straßenbaumaßnahmen eine geotechnisch geeignete und möglichst sichere Trassenführung zu finden. Redaktionsschluss: 06.12.2022

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

The variation of rock strength and stiffness, known as mechanical anisotropy, is expected at different scales: large (rock mass) - or small (intact rock) - scales. It is always mandatory for engineering applications built either on or in anisotropic rock masses to investigate the strength and deformation behavior of those masses. To achieve this goal, continuum-based constitutive models are presented to analyze the mechanical anisotropy. One of both implemented models is named ‘Transubi model’ which considers the transverse isotropic elasticity into bi-linear Mohr-Coulomb strain hardening/softening plastic framework. Experimental investigations and numerical simulations focused mainly on the influence of the mechanical anisotropy on the plastic zoning around excavated openings in laminated rocks. Later, the Transubi model was applied to a tunnel excavated in a shaly facies formation of bedded argillaceous Opalinus clay in an URL (FE-tunnel) to obtain the short-term stability insights. Overall, the research outcomes may have a prospective impact regarding the understanding of anisotropy of laminated, bedded and foliated rocks which improves the deformation behaviour predictability using continuum-based numerical modeling tools.