Potential coordinate mislocations in crosshole tomography: Results from the Grimsel test site, Switzerland

Geophysics ◽  
1997 ◽  
Vol 62 (6) ◽  
pp. 1696-1709 ◽  
Author(s):  
Hansruedi Maurer ◽  
Alan G. Green
Keyword(s):  
Radioactive Waste ◽  
Test Site ◽  
Swiss Alps ◽  
Low Velocity ◽  
Weak Anisotropy ◽  
Data Set ◽  
Tomographic Images ◽  
Wide Range ◽  
Grimsel Test Site ◽  
National Cooperative

Tomographic techniques based on borehole‐to‐borehole and tunnel‐to‐borehole traveltime data are now being employed in a wide range of studies associated with the exploration and exploitation of hydrocarbons and metallic minerals, the disposal of chemical and radioactive waste, diverse civil engineering projects, and archaeology. A fundamental assumption of currently employed tomographic inversion strategies is that the coordinates of the boreholes and tunnels containing the seismic sources and receivers are accurately known. By inverting both synthetic and observed traveltime data, we demonstrate that relatively minor coordinate errors (1–2%) in the deeper parts of long boreholes (>100 m) may produce artifacts in the tomographic images that are comparable in extent and amplitude to true velocity anomalies. To address this problem, we introduce the coupled inverse method, commonly used in earthquake studies, as a means to determine simultaneously borehole coordinate adjustments and an estimate of the tomographic image. This method has been applied to traveltime data generated and collected along a tunnel and in three boreholes within a granitic body situated in the central Swiss Alps (Grimsel test site operated by NAGRA, the Swiss National Cooperative for the Disposal of Radioactive Waste). Coupled inversions of two independent subsets of traveltime data that involve a common central borehole, together with a coupled inversion of the entire data set, yield consistent coordinate adjustments for all boreholes and tomographic images that are compatible with the known geology and a sonic log from the central borehole. Further tests with synthetic data demonstrate that certain types of weak anisotropy could influence the coupled inversions. Regardless of whether minor coordinate mislocations or weak anisotropy is the dominant effect at the Grimsel test site, distinct low‐velocity zones appear to delineate fractures zones that are conduits for groundwater flow.

Crosshole GPR full-waveform inversion of waveguides acting as preferential flow paths within aquifer systems

Geophysics ◽  
2012 ◽  
Vol 77 (4) ◽  
pp. H57-H62 ◽  
Author(s):  
Anja Klotzsche ◽  
Jan van der Kruk ◽  
Giovanni Meles ◽  
Harry Vereecken
Keyword(s):  
Preferential Flow ◽  
Waveform Inversion ◽  
Clay Content ◽  
Test Site ◽  
Full Waveform Inversion ◽  
Depth Range ◽  
Low Velocity ◽  
Full Waveform ◽  
Aquifer Systems ◽  
Wide Range

High-contrast layers caused by porosity or clay content changes can have a dominant effect on hydraulic processes within an aquifer. These layers can act as low-velocity waveguides for GPR waves. We used a field example from a hydrological test site in Switzerland to show that full-waveform inversion of crosshole GPR signals could image a subwavelength thickness low-velocity waveguiding layer. We exploited the full information content of the data, whereas ray-based inversion techniques are not able to image such thin waveguide layers because they only exploit the first-arrival times and first-cycle amplitudes. This low-velocity waveguide layer is caused by an increase in porosity and indicates a preferential flow path within the aquifer. The waveguide trapping causes anomalously high amplitudes and elongated wavetrains to be observed for a transmitter within the waveguide and receivers straddling the waveguide depth range. The excellent fit of amplitudes and phase between the measured and modeled data confirms its presence. This new method enables detailed aquifer characterization to accurately predict transport and flow and can be applied to a wide range of geologic, hydrological, and engineering investigations.

Grimsel Test Site - Phase VI: Review of Accomplishments and Next Generation of In-Situ Experiments Under Repository Relevant Boundary Conditions

2008 ◽  
Vol 1107 ◽  
Author(s):  
Ingo Blechschmidt ◽  
Stratis Vomvoris ◽  
Joerg Rueedi ◽  
Andrew James Martin
Keyword(s):  
Near Field ◽  
Planning Horizon ◽  
Test Site ◽  
Low Ph ◽  
Swiss Alps ◽  
In Situ Experiments ◽  
Grimsel Test Site ◽  
And Migration

AbstractThe Grimsel Test Site owned and operated by Nagra is located in the Swiss Alps (www.grimsel.com). The Sixth Phase of investigations was started in 2003 with a ten-year planning horizon. With the investigations and projects of Phase VI the focus has shifted more towards projects assessing perturbation effects of repository implementation and projects evaluating and demonstrating engineering and operational aspects of the repository system. More than 17 international partners participate in the various projects, which form the basic organisational “elements” of Phase VI. Scientific and engineering interaction among the different projects is ensured via an annual meeting and several experimental team meetings throughout the year. On-going projects include: evaluation of full-scale engineered systems under simulated heat production and long-term natural saturation (NF-Pro/FEBEX), gas migration through engineered barrier systems (GMT, finished this year), emplacement of a shotcrete low-pH plug (ESDRED/Module IV), testing and evaluation of standard monitoring techniques (TEM).Numerous in-situ experiments with inactive tracers and radionuclides were successfully carried out over the past few years at the Grimsel Test Site (GTS). For the GTS Phase VI, three major projects have been initiated to simulate the long-term behaviour of contamination plumes in the repository near-field and the surrounding host rock:•The CFM (Colloid Formation and Migration) project, which focuses on colloid generation and migration from a bentonite source doped with radionuclides•The LCS (Long-Term Cement Studies) project, which aims at improving the understanding of low-pH cement interaction effects in water conducting features•The LTD (Long-Term Diffusion) project, which aims at in-situ verification of long-term diffusion concepts for radionuclidesAs Phase VI approaches its mid-term point, what are the next steps planned? The accomplishments assessed to date and the opportunities with the on-going projects as well as new projects – currently under discussion – are presented herein

U, Th, Eu and colloid mobility in a granite fracture under near-natural flow conditions

2004 ◽  
Vol 92 (9-11) ◽  
Author(s):  
Thorsten Schäfer ◽  
Horst Geckeis ◽  
Muriel Bouby ◽  
Thomas Fanghänel
Keyword(s):  
Flow Velocity ◽  
Test Site ◽  
Swiss Alps ◽  
Flow Conditions ◽  
Grimsel Test Site ◽  
Natural Flow ◽  
Core Migration ◽  
Colloid Mobility

SummaryLaboratory core migration experiments were performed in a granite fracture from the Grimsel Test Site (GTS, central Swiss Alps). The flow velocity was varied (46 m yr

scholarly journals Bayesian full-waveform inversion of tube waves to estimate fracture aperture and compliance

Solid Earth ◽  
2020 ◽  
Vol 11 (2) ◽  
pp. 657-668 ◽  
Author(s):  
Jürg Hunziker ◽  
Andrew Greenwood ◽  
Shohei Minato ◽  
Nicolás Daniel Barbosa ◽  
Eva Caspari ◽  
...  
Keyword(s):  
Waveform Inversion ◽  
Test Site ◽  
Hydrocarbon Exploration ◽  
Swiss Alps ◽  
Fracture Aperture ◽  
Full Waveform ◽  
Wide Range ◽  
Hydraulic Aperture ◽  
Vsp Data ◽  
Tube Wave

Abstract. The hydraulic and mechanical characterization of fractures is crucial for a wide range of pertinent applications, such as geothermal energy production, hydrocarbon exploration, CO2 sequestration, and nuclear waste disposal. Direct hydraulic and mechanical testing of individual fractures along boreholes does, however, tend to be slow and cumbersome. To alleviate this problem, we propose to estimate the effective hydraulic aperture and the mechanical compliance of isolated fractures intersecting a borehole through a Bayesian Markov chain Monte Carlo (MCMC) inversion of full-waveform tube-wave data recorded in a vertical seismic profiling (VSP) setting. The solution of the corresponding forward problem is based on a recently developed semi-analytical solution. This inversion approach has been tested for and verified on a wide range of synthetic scenarios. Here, we present the results of its application to observed hydrophone VSP data acquired along a borehole in the underground Grimsel Test Site in the central Swiss Alps. While the results are consistent with the corresponding evidence from televiewer data and exemplarily illustrate the advantages of using a computationally expensive stochastic, instead of a deterministic inversion approach, they also reveal the inherent limitation of the underlying semi-analytical forward solver.

Comparison of high‐frequency seismic sources at the Grimsel test site, central Alps, Switzerland

Geophysics ◽  
1998 ◽  
Vol 63 (4) ◽  
pp. 1363-1370 ◽  
Author(s):  
Jan Bühnemann ◽  
Klaus Holliger
Keyword(s):  
High Frequency ◽  
Shear Zones ◽  
Test Site ◽  
Radioactive Waste Disposal ◽  
Swiss Alps ◽  
P Wave ◽  
Seismic Sources ◽  
Rock Body ◽  
Grimsel Test Site ◽  
Explosive Charges

In August 1995, various high‐frequency seismic sources were tested at the Grimsel Test Site (GTS), located inside a crystalline rock body in the central Swiss Alps. These source tests were designed to facilitate future tomographic studies of potential radioactive waste disposal sites. The principal objective was to identify borehole and tunnel seismic sources capable of generating powerful high‐frequency signals such that frequencies up to 1000 Hz can be observed over distances of 1000 m in crystalline or consolidated sedimentary rocks. Seismic sources were situated in water‐filled boreholes (sparker, two piezoelectric sources, explosives) and at or near the tunnel wall (accelerated weight drop, minivibrator, bolt gun, buffalo gun, explosives). To evaluate and compare the source characteristics, the direct P-wave generated by the various seismic sources was investigated for the decay of its S/N and dominant frequency with offset and for the maximum distance at which first arrivals could be picked. Of the seismic sources tested, small explosive charges (5–100 g) had the most favorable S/N and frequency characteristics. At GTS, the target distance (∼1000 m) was reached with explosive charges of 50 g or more. None of the sources tested was capable of generating signals that sustained frequencies of 1000 Hz over distances in excess of 100 to 200 m. The unusually strong attenuation implied by this observation is likely due to the fact that the rocks at GTS underwent brittle deformation during the Alpine orogeny and therefore contain numerous fractures and shear zones.

Grimsel 2000 – Status of International Projects at the Grimsel Test Site (GTS)

2000 ◽  
Vol 663 ◽  
Author(s):  
W. Kickmaier ◽  
W. R. Alexander ◽  
S. Vomvoris ◽  
I.G. McKinley
Keyword(s):  
Performance Assessment ◽  
Test Site ◽  
Swiss Alps ◽  
Geological Environment ◽  
Grimsel Test Site ◽  
Fundamental Understanding ◽  
International Projects ◽  
Integrated Performance ◽  
Future Work ◽  
Integrated Performance Assessment

ABSTRACTDuring 17 years of cooperation, the Grimsel underground test site in the Swiss Alps has become established as a major center for study of the deep geological environment. The present Phase V of operation involves collaboration of 15 organizations from 9 countries.The 7 major projects currently running can be divided into 3 areas:- Confirmation of fundamental understanding and testing of models of processes identified to be significant in integrated performance assessment- Demonstration and optimization of site characterization technology- Demonstration of the technology for constructing and operating a deep repository in an efficient and quality assured manner.This sub-division of projects is somewhat simplistic as, wherever possible, large, long- running experiments are designed to achieve a number of goals. The paper will provide a summary of some projects running at Grimsel, an overview of the rationale behind the experimental concepts and a perspective on possible future work.

scholarly journals Bayesian full-waveform inversion of tube waves to estimate fracture aperture and compliance

2019 ◽  
Author(s):  
Jürg Hunziker ◽  
Andrew Greenwood ◽  
Shohei Minato ◽  
Nicolas D. Barbosa ◽  
Eva Caspari ◽  
...  
Keyword(s):  
Waveform Inversion ◽  
Test Site ◽  
Hydrocarbon Exploration ◽  
Swiss Alps ◽  
Fracture Aperture ◽  
Full Waveform ◽  
Wide Range ◽  
Hydraulic Aperture ◽  
Vsp Data ◽  
Tube Wave

Abstract. The hydraulic and mechanical characterization of fractures is crucial for a wide range of pertinent applications, such as, for example, geothermal energy production, hydrocarbon exploration, CO2-sequestration, and nuclear waste disposal. Direct hydraulic and mechanical testing of individual fractures along boreholes does, however, tend to be slow and cumbersome. To alleviate this problem, we propose to estimate the effective hydraulic aperture and the mechanical compliance of isolated fractures intersecting a borehole through a Bayesian Markov chain Monte Carlo (MCMC) inversion of full-waveform tube-wave data recorded in a vertical seismic profiling (VSP) setting. The solution of the corresponding forward problem is based on a recently developed semi-analytical solution. This inversion approach has been tested for and verified on a wide range of synthetic scenarios. Here, we present the results of its application to observed hydrophone VSP data acquired along a borehole in the underground Grimsel Test Site in the Central Swiss Alps. While the results are consistent with the corresponding evidence from televiewer data and exemplarily illustrate the advantages of using a computationally expensive stochastic, instead of a deterministic, inversion approach, they also reveal the inherent limitation of the underlying semi-analytical forward solver.

Grimsel Test Site - The Next Decades

2002 ◽  
Vol 757 ◽  
Author(s):  
Stratis Vomvoris ◽  
Wolfgang Kickmaier ◽  
Ian G. McKinley
Keyword(s):  
Radioactive Waste ◽  
Waste Management ◽  
Time Scales ◽  
Test Site ◽  
Radioactive Waste Management ◽  
Grimsel Test Site

ABSTRACTThe Grimsel Test Site, which has been in operation since 1984, is known in the radioactive waste management community for the scope and quality of the experiments and projects performed over the last two decades. This paper will overview Nagra's commitments and the current plans for future activities in association with Grimsel, which are being developed considering time scales of the order of a decade or more.

Grimsel Test Site — Phase VI: Review of Accomplishments and Next Steps

2007 ◽  
Author(s):  
Stratis Vomvoris ◽  
Wolfgang Kickmaier
Keyword(s):  
Ad Hoc ◽  
Field Testing ◽  
Planning Horizon ◽  
Test Site ◽  
Swiss Alps ◽  
Tracer Transport ◽  
Geophysical Investigation ◽  
Grimsel Test Site

The Grimsel Test Site owned and operated by Nagra is located in the Swiss Alps (www.grimsel.com). The sixth Phase of investigations was started in 2003 with a ten-year planning horizon. With the investigations and projects of Phase VI the focus is shifted more towards projects assessing perturbation effects of repository implementation and projects evaluating and demonstrating engineering and operational aspects of the repository system. More than 17 international partners participate in the various projects, which form the basic organisational ‘elements’ of Phase VI, each one further structured in field-testing, laboratory studies, design and modelling tasks, as appropriate. Each project phase is planned with a duration of 3 to 5 years, to facilitate all practical and administrative aspects, ensuring flexibility for updating the overall plan with the recent findings. Scientific and engineering interaction among the different projects is ensured via the annual international meeting and ad-hoc meetings, as appropriate. As Phase VI approaches its mid-term point, a review of the accomplishments to date is performed to provide a sound basis for the detailed planning of the next steps. The accomplishments to date are described and assessed below; the opportunities with the on-going projects as well as new projects – currently under discussion – are also presented and discussed. The on-going projects include: studies of the long-term diffusion with emphasis on the processes in the rock matrix (LTD); colloid studies under in-situ generation conditions and migration velocities closer to velocities expected in an actual repository site (CFM); studies of the long-term cement interactions with natural systems (LCS); evaluation of full-scale engineered systems under simulated heat production and long-term natural saturation (NF-Pro/FEBEX); gas migration through engineered barrier systems (GMT); emplacement of shotcrete low-pH plug (ESDRED/Module IV); test and evaluation of monitoring systems (TEM). In addition, various shorter term projects assessing, for example, new geophysical investigation tools, wireless transmission, testing new tools and training for in-situ tracer transport studies have been performed and/or are planned for the near future.

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