scholarly journals From process to system understanding with multi-disciplinary investigation methods: set-up and first results of the CD-A experiment (Mont Terri rock laboratory)

2021 ◽  
Vol 1 ◽  
pp. 79-81
Author(s):  
Gesa Ziefle ◽  
Tuanny Cajuhi ◽  
Sebastian Condamin ◽  
Stephan Costabel ◽  
Oliver Czaikowski ◽  
...  
Keyword(s):  
Radioactive Waste ◽  
Site Selection ◽  
Fault Zones ◽  
Rock Laboratory ◽  
Investigation Methods ◽  
Physical Effects ◽  
Mont Terri ◽  
Mont Terri Rock Laboratory ◽  
The Impact

Abstract. A potential repository site for high-level radioactive waste should ensure the highest possible safety level over a period of one million years. In addition to design issues, demonstrating the integrity of the barrier is essential as it ensures the long-term containment of radioactive waste. Therefore, a multi-disciplinary approach is necessary for the characterization of the surrounding rock and for the understanding of the occurring physical processes. For site selection, however, the understanding of the respective system is essential as well: Do fault zones exist in the relevant area? Are these active and relevant for interpreting system behavior? What is the role of the existing heterogeneities of the claystone and how do these site-dependent conditions influence the physical effects? To answer these questions, the site-selection procedure requires underground exploration, which includes geophysical and geological investigations on milli- to decameter scales. Their results serve as the basis for numerical modelling. This combined, multi-disciplinary interpretation requires extensive knowledge of the various methods, their capabilities, limitations, and areas of application. In the cyclic deformation (CD-A) experiment in the Mont Terri rock laboratory, the hydraulic–mechanical effects due to excavation and the climatic conditions within the rock laboratory are investigated in two niches in the Opalinus Clay. The twin niches differ mainly with regard to the relative humidity inside them, but are also characterized by different boundary conditions such as existing fault zones, the technical construction of the neighboring gallery, etc. In order to gain insights into the relevance of the individual influences, comparative studies are being carried out on both niches. The presented results provide a first insight into the initial experimental years of the CD-A long-term experiment and illustrate the benefits of multi-disciplinary investigations in terms of system understanding and the scale dependency of physical effects. Amongst other effects, the assessment of the impact of heterogeneities on the deformation behavior and the evolution of pore water pressure is very complex and benefits from geological interpretation and measurements of for example deformation, water content, and pore pressure. The numerical modeling allows statements about the interaction of different processes and thus enables an interpretation of the overall system, taking into account the knowledge gained by the multi-disciplinary investigation.

scholarly journals Active seismic monitoring of CO2-saturated brine injection into a fault (CS-D experiment in the Mont Terri Rock Laboratory)

2020 ◽  
Author(s):  
Melchior Grab ◽  
Alba Zappone ◽  
Antonio P. Rinaldi ◽  
Sebastian Hellmann ◽  
Quinn Wenning ◽  
...  
Keyword(s):  
Saturated Formation ◽  
Second Phase ◽  
Formation Water ◽  
Rock Laboratory ◽  
Imaging Results ◽  
Geophysical Surveys ◽  
Abstract Submission ◽  
Mont Terri ◽  
Mont Terri Rock Laboratory

<p>Confirming the permanent containment is a key challenge for the storage of CO<sub>2 </sub>in deep underground reservoirs. Faults in the cap rock of such reservoirs are potential flow paths for the CO<sub>2</sub> to escape. Our decametre-scale experiment at the Mont Terri Rock Laboratory aims to better understand mechanisms of CO<sub>2</sub> leakage trough a fault, and to test strategies to monitor the propagation of CO<sub>2</sub>-saturated water through faults.</p><p>Two boreholes were drilled through the main fault in Mont Terri with packer-intervals dedicated to fluid-injection and hydraulic/geochemical monitoring. Another five boreholes in the close surrounding were equipped with various instruments for geotechnical and geophysical observations. During the first phase of the experiment, the hydraulic response of the fault was characterized with injections of formation water in a step-up mode at pressures up to 6.0 MPa. The second phase, which was still on-going at the time of the abstract submission, consists of a long-term (several months) injection of CO<sub>2</sub>-saturated formation water at a constant head of 4.5 MPa, which is below the fault opening pressure. All injection activities were monitored with active seismic measurements, along with a comprehensive set of hydraulic-, mechanical-, geochemical- and other geophysical surveys. We will present the active seismic imaging results from the step-up injection test and compare them with the other surveys. Additionally, preliminary results will be shown acquired during the long-term injection of CO<sub>2</sub>-saturated formation water into the fault.</p>

Tiltmeter Measurements at the Underground Rock Laboratory in Mont Terri

2020 ◽  
Author(s):  
Dorothee Rebscher
Keyword(s):  
Decadal Variability ◽  
Opalinus Clay ◽  
Earthquake Activity ◽  
Rock Laboratory ◽  
In Situ Experiments ◽  
First Results ◽  
Mont Terri ◽  
Mont Terri Rock Laboratory

<p>Mont Terri rock laboratory, located in the Swiss Jurassic Mountains, was established with the focus on the investigation and analysys of the properties of argillaceous formations. The scope of Opalinus Clay as a safe, potential option for nuclear waste disposal was broaden, as the behaviour of claystone is of high interest also in the context of caprocks, and hence, for many dynamical processes in the subsurfaces. Extensive research has been performed already for more than 20 years by the partners of the Mont Terri Consortium. These close cooperations cover a broad range of scientific aspects using numerical modelling, laboratory studies, and last not least in-situ experiments. Here, included in the long-term monitoring programme, new investigations apply tiltmeters. Since April 2019, platform tiltmeters have been installed at various locations within the galleries and niches of Mont Terri. The biaxial instruments have resolutions of 1 nrad and 0.1 µrad, respectively (Applied Geomechanics and Lippmann Geophysikalische Messgeräte). The tilt measurements are embedded within various experiments contributing to specific, multiparametrical studies. However, the growing tilt network as a whole will also provide novel information of the rock laboratory. The different time-scales of interest include long-term observations of yearly and decadal variability. So far tilt signals were identified due to excavations during the recent enlargement of the laboratory, earthquake activity (Albania), and local effects. First results of these quasi-continuous recordings will be presented.</p>

Investigations based on biaxial tiltmeter array and uniaxial hydrostatic levelling system at the Mont Terri rock laboratory

2021 ◽  
Author(s):  
Dorothee Rebscher ◽  
Yves Guglielmi ◽  
Inma Gutierrez ◽  
Edi Meier ◽  
Senecio Schefer
Keyword(s):  
Underground Laboratory ◽  
Dynamical Processes ◽  
Rock Laboratory ◽  
Spatial Coverage ◽  
History Of ◽  
Fruitful Cooperation ◽  
Mont Terri ◽  
Mont Terri Rock Laboratory ◽  
Scientific Questions

<p>In order to enable investigations and further comprehensive understanding of dynamical processes, it is clear one has to identify all relevant parameters and aim to record them all under best conditions concerning e.g. resolution, coverage in space, and in many cases on a multitude of scales in time. Obviously, it is also difficult to satisfy all these constrains in full. Especially scientific long-term observations often suffer the lack of necessary lasting commitment; secure funding, continual high quality maintenance, protected environment, or sufficient planning stability. Fortunately, the Swiss Mont Terri rock laboratory, with its history of now 25 years of forefront scientific expertise, a long-standing fruitful cooperation formed by the partners of the consortium and in consequence thereof state-of-the-art results obtained through 100 completed individual experiments and 45 additional experiments actually ongoing, ensures the conditions listed above.</p><p>Based on this favorable prospect, a now growing tiltmeter array is established at the underground laboratory. The instruments are embedded in several multidisciplinary experiments, dedicated to numerous, different scientific questions. Starting in April 2019, the first two platform tiltmeters became operational. Less than two years later, ten biaxial instruments are quasi-continuously monitoring deformation at various locations within the galleries and niches at Mont Terri. The envisioned, increasing spatial coverage of the network will facilitate geodetic observations of the underground rock laboratory as a whole and of its subregions as well.</p><p>Already in September 2012, a 50 m long hydrostatic levelling system (HLS) was installed along a gallery in the underground laboratory to detect displacements across an active geological fault zone. The combination of both, i.e. the uniaxial, integral deformations data provided by HLS together with the array of biaxial, point measurements acquired by the tiltmeters offers a unique concerted opportunity to achieve detailed deformation data in a large underground rock laboratory and to survey the associated dynamical processes occurring on timeframes covering seconds to decades.</p>

scholarly journals An interdisciplinary view of the long-term evolution of repository systems across scales: the iCROSS project

2021 ◽  
Vol 1 ◽  
pp. 85-87
Author(s):  
Dirk Bosbach ◽  
Horst Geckeis ◽  
Frank Heberling ◽  
Olaf Kolditz ◽  
Michael Kühn ◽  
...  
Keyword(s):  
Radioactive Waste ◽  
Field Experiments ◽  
Coupled Processes ◽  
Nuclear Waste Repository ◽  
Radionuclide Transport ◽  
Clay Rock ◽  
Rock Characterization ◽  
Mont Terri ◽  
The Impact

Abstract. The interdisciplinary project “Integrity of nuclear waste repository systems – Cross-scale system understanding and analysis (iCROSS)” combines research competencies of Helmholtz scientists related to the topics of nuclear, geosciences, biosciences and environmental simulations in collaborations overarching the research fields energy and earth and environment. The focus is to understand and analyze close-to-real long-term evolutionary pathways of radioactive waste repositories across nanoscales to repository scales. The project is subdivided into work packages dealing with laboratory studies, field experiments in underground research laboratories (URLs), advanced modelling studies and the integration and alignment of data and information using virtual reality methods. In this sense, the project structure aims at a holistic view on relevant processes across scales in order to comprehensively simulate potential repository evolutions. Within the multi-barrier system of a repository for heat-generating radioactive waste, a number of complex reactions proceed, including dissolution, redox processes, biochemical reactions, gas evolution and solid/liquid interface and (co)precipitation reactions. At the same time, thermal and external mechanical stress has an impact on the conditions in a deep geological repository. All those processes are highly coupled, with multiple interdependencies on various scales and have a strong impact on radionuclide mobility and retention. In recent years, substantial progress was achieved in describing coupled thermal-hydro-mechanical-chemical-biological (THM/CB) processes in numerical simulations. A realistic and concise description of these coupled processes on different time and spatial scales is, at present, a largely unresolved scientific and computational challenge. The close interaction of experimental and simulation teams aims at a more accurate quantification and assessment of processes and thus, the reduction of uncertainties and of conservative assumptions and eventually to a close-to-real perception of the repository evolution. One focus of iCROSS is directed to relevant processes in a clay rock repository. In this context, the iCROSS team became a full member of the international Mont Terri consortium and worked in close collaboration with international and German institutions in URL projects. Respective experiments specifically deal with coupled processes at the reactive interfaces in a repository near field (e.g. the steel/bentonite and bentonite/concrete interfaces). Within iCROSS, the impact of secondary phase formation on radionuclide transport is investigated. At Mont Terri, experiments are in preparation to study radionuclide transport phenomena in clay rock formations within temperature gradients and in facies exhibiting significant heterogeneities on different scales (nm to cm). Beside those studies, high resolution exploration methods for rock characterization are developed and tested and the effect of temperature and other boundary conditions on the strength, creep properties and healing of faults within Opalinus clay are quantified. Multiphysics models coupled to reactive transport simulation have been further developed and applied to laboratory and field experiments. Results are digitally analyzed and illustrated in a visualization center, in order to enhance the comprehension of coupled processes in repository systems across scales. The present contribution provides an overview on the project and reports selected results. The impact of considering complex coupled processes in repository subsystems for the assessment of the integrity of a given (generic) repository arrangement is discussed.

scholarly journals Coupled HM modeling assists in designing CO2 long-term periodic injection experiment (CO2LPIE) in Mont Terri rock laboratory 

2021 ◽  
Author(s):  
Dario Sciandra ◽  
Víctor Vilarrasa ◽  
Iman Rahimzadeh Kivi ◽  
Roman Makhnenko ◽  
Christophe Nussbaum ◽  
...  
Keyword(s):  
Lag Time ◽  
Opalinus Clay ◽  
Bedding Planes ◽  
Rock Laboratory ◽  
Hydraulic Anisotropy ◽  
The One ◽  
Mont Terri ◽  
Mont Terri Rock Laboratory ◽  
Injection Experiment

<p>We are performing a series of coupled hydro-mechanical (HM) simulations to model CO<sub>2</sub> flow through Opalinus Clay at the Mont Terri rock laboratory in the CO<sub>2</sub> Long-term Periodic Injection Experiment (CO<sub>2</sub>LPIE). CO<sub>2</sub>LPIE aims at inter-disciplinary investigations of the caprock sealing capacity in geologic CO<sub>2</sub> storage in a highly monitored environment at the underground laboratory scale. Numerical modeling allows us to gain knowledge on the dynamic processes resulting from CO<sub>2</sub> periodic injection and to assist the experimental design. The cyclic injection parameters (i.e., the period and the amplitude) have to be optimized for the field experiment and therefore different values are taken into account. Opalinus Clay is a claystone with nanoDarcy permeability that contains well developed bedding planes responsible for its anisotropic HM behavior. The hydraulic anisotropy is defined by a permeability parallel to the bedding planes being three times the one perpendicular to it. Additionally, the drained Young’s modulus is measured to be 1.7 GPa parallel and 2.1 GPa perpendicular to bedding. Excavation reports by swisstopo document a SSE-dip of 45° for the bedding planes at the experiment location. CO<sub>2</sub> injection generates a mean overpressure of 1 MPa into the brine that propagates into the formation. The differential pressure between CO<sub>2</sub> and formation water, i.e., capillary pressure, is lower than the entry pressure and thus, CO<sub>2</sub> diffuses through the pores but does not advect in free phase. The liquid overpressure distribution is distorted by the hydraulic anisotropy, preferentially advancing along the bedding planes, as the associated permeability is higher than the one perpendicular to the bedding. The pore pressure buildup induces a poromechanical stress increase and an expansion of the rock that leads to a permeability enhancement of up to two orders of magnitude. The cyclic stimulation propagates trough the domain faster and with a lag time and an attenuation, both of which increase with distance from the source with, their values being dependent on permeability, porosity and stiffness of the rock. As a result of the model orthotropy, the attenuation and the lag time change with direction, i.e. they are higher in the direction perpendicular to the bedding and lower in the direction parallel to the bedding. Given the very low permeability of Opalinus Clay, the overpressure generated requires a long time to diffuse into the rock. Furthermore, the amplitude attenuation dissipates quite rapidly, so monitoring wells should be placed as close to the injection well as possible. The study of amplitude attenuation and time lag is necessary to determine how they can be utilized to evaluate the evolution of the HM properties as the rock is altered by the acidic nature of CO<sub>2</sub>-brine mixture Comparison between field data and numerical simulations will be a useful asset to fill the gap.</p>

scholarly journals Understanding the evolution of nuclear waste repositories by performing appropriate experiments – selected investigations at Mont Terri rock laboratory

2019 ◽  
Vol 49 ◽  
pp. 175-186
Author(s):  
Kristof Schuster ◽  
Markus Furche ◽  
Hua Shao ◽  
Jürgen Hesser ◽  
Jan-Martin Hertzsch ◽  
...  
Keyword(s):  
Site Selection ◽  
Selection Process ◽  
Opalinus Clay ◽  
Rock Laboratory ◽  
Federal Institute ◽  
Argillaceous Rocks ◽  
Equilibrium Phases ◽  
High Level ◽  
Mont Terri ◽  
Mont Terri Rock Laboratory

Abstract. Any site selection process for a final repository for high-level and heat producing radioactive waste is a national challenge and has to take into account, among others, regional geological settings. In Germany, the site selection has to restart from zero, and all potential host rocks have to be considered equal, including argillaceous rocks. Therefore, the Federal Institute for Geosciences and Natural Resources (BGR) performs appropriate experiments in the Swiss Mont Terri rock laboratory, which is located in the Jurassic Opalinus Clay. In this paper, activities and results from actual and still ongoing experiments, with participation of BGR, are presented exemplarily. All experiments aim for a contribution to understand particular aspects regarding the behaviour of underground facilities, BGR's focus lies mainly on aspects of the early lifetime of a repository, namely the construction, post-closure transient, and partly post-closure equilibrium phases. It is obvious that for a full understanding of the evolution of a final repository, knowledge and experience of many different groups, their studies and results covering all aspects, have to be included. In this paper, we can only emphasise a few representative examples on geophysical and geotechnical in-situ site investigations, geotechnical mine-by monitoring, laboratory investigations, and modelling aspects. The combined interpretation of these results enhance interpretations and is a prerequisite for a comprehensive understanding of a repository.

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