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

Confirming the permanent containment is a key challenge for the storage of CO2 in deep underground reservoirs. Faults in the cap rock of such reservoirs are potential flow paths for the CO2 to escape. Our decametre-scale experiment at the Mont Terri Rock Laboratory aims to better understand mechanisms of CO2 leakage trough a fault, and to test strategies to monitor the propagation of CO2-saturated water through faults.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&#160;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 CO2-saturated formation water at a constant head of 4.5&#160;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 CO2-saturated formation water into the fault.

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

Safety of Nuclear Waste Disposal ◽

10.5194/sand-1-79-2021 ◽

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.

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Tiltmeter Measurements at the Underground Rock Laboratory in Mont Terri

10.5194/egusphere-egu2020-11965 ◽

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

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 &#181;rad, respectively (Applied Geomechanics and Lippmann Geophysikalische Messger&#228;te). 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.

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

10.5194/egusphere-egu21-8624 ◽

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

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&#160;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&#160;completed individual experiments and 45&#160;additional experiments actually ongoing, ensures the conditions listed above.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.Already in September 2012, a 50&#160;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.

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

10.5194/egusphere-egu21-8982 ◽

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

We are performing a series of coupled hydro-mechanical (HM) simulations to model CO2 flow through Opalinus Clay at the Mont Terri rock laboratory in the CO2 Long-term Periodic Injection Experiment (CO2LPIE). CO2LPIE aims at inter-disciplinary investigations of the caprock sealing capacity in geologic CO2 storage in a highly monitored environment at the underground laboratory scale. Numerical modeling allows us to gain knowledge on the dynamic processes resulting from CO2 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&#8217;s modulus is measured to be 1.7&#160;GPa parallel and 2.1&#160;GPa perpendicular to bedding. Excavation reports by swisstopo document a SSE-dip of 45&#176; for the bedding planes at the experiment location. CO2 injection generates a mean overpressure of 1 MPa into the brine that propagates into the formation. The differential pressure between CO2 and formation water, i.e., capillary pressure, is lower than the entry pressure and thus, CO2 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 CO2-brine mixture Comparison between field data and numerical simulations will be a useful asset to fill the gap.

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