We have published the first issue of the BedrettoLab newsletter. In this issue, you will take a glimpse into the deep underground, learn more about the Bedretto Reservoir Project and discover how we collect data at the BedrettoLab.
After almost two years of intense work to build the stimulation and monitoring boreholes, the drilling campaign has been finished last week by cementing a steel-casing in ST2. By now, nine boreholes with a total length of some 2’500 meters drilled have been completed - an impressive achievement!
For the drilling in Bedretto a completely new drill-rig has been engineered and was transported brand-new on-site in 2020. Now, after successful completion the drill-rig and its equipment were dismantled, moved out of the tunnel and are now being returned to the drilling company's warehouse.
Currently, the new boreholes are being prepared for the instrumentation, which will start in July 2021. 11 June 2021
The brand-new drill-rig arrives on site.
The new equipment upon delivery.
The drill-rig and the equipment after completion of the drilling campaign.
As part of the ongoing Bedretto Reservoir Project, high-resolution seismic networks have been installed along the Bedretto main tunnel and in dedicated boreholes to monitor the behaviour of the rock volume and the possible occurrence of seismicity.
The water injections performed in the past two weeks by Geo Energie Suisse (GES) induced numerous very small earthquakes in the vicinity of the borehole – an expected and desired effect of the stimulations. The last stimulation activities took place three days ago, and the induced seismicity near the injection borehole has since decreased and ceased.
The seismic network allows to detect events in the whole tunnel area, and on the night of 6 May 2021, a couple of events have been registered at about 500 meters away from the injection area, in the direction of the entrance of the Bedretto tunnel. The largest event had a magnitude of +0.1, according to the Swiss Seismological Service at ETH Zurich. Therewith, this event is considerably lower than the magnitude threshold above which people can usually notice an earthquake. Only the very dense seismic monitoring system made it possible to record and locate such small events. A full analysis of the data recorded over the past weeks enabled us to detect so far nine events with magnitudes down to ML= -1.8, some of which occurring already several months before the start of the water injections.
Although these events are too small to raise any immediate safety concerns, they provide a unique possibility to understand how pressure perturbations connected to activities in the reservoir and to water flow propagate through the rock volume. The BedrettoLab team has initiated a range of investigations to gain a better understanding of the causes of these unusual events and will use this new knowledge to steer future stimulation activities. 7 May 2021
Update 12 May 2021: Detective work continues
The Bedretto team continues to investigate the micro-earthquakes observed first on May 6th. In the past five days, three events with a maximum magnitude of -0.5 were observed, plus one event at more than 1 km from the tunnel. Using additional reprocessing steps, the team was able to reconstruct the timeline of the earthquakes of the past two years in more detail. Seismologists use an approach called “template matching”: Once a signal is known, they can scan past data for similar patterns that could not be detected before. This analysis revealed that another seismicity episode occurred unknown to the Bedretto team in October 2020 a few hundred meters further into the tunnel as compared to the May 6th events, with a maximum magnitude of about 0.2. However, as early as March 2020, another episode of very small events of magnitude -1.5 and smaller was detected.
So far, the events in March and October 2020 seem to have no obvious connection to drilling or stimulation activities in the Lab. The events in October followed within a few days of extreme rainfall at Bedretto, so it is possible that the seismicity is related to changes in pore pressures induced by rainfall, but other sequences do not so clearly correlate. Rain induced earthquakes have been observed in other parts of Switzerland (see for example here), mainly in Karst areas where water from the surface can quickly reach seismogenic depths of 1 kilometre or more.
The detective work therefore continues: The Bedretto team is installing additional seismic stations, gathering fluid samples and is re-analysing data, and they are considering hydro-mechanic models to build plausible models for the micro-earthquakes. At the same time, activities in the tunnel continue with microdrilling, notching and stress measurements in one of the long boreholes; activities that do not result in any micro-seismicity. Injections are not planned for the next days.
Update 27 May 2021: Clues found, investigations continue
The detective work on the cause of the observed micro-earthquakes has produced some clues, but further analysis is necessary to better understand the seismicity around the BedrettoLab.
One of the clues is that much of the observed seismicity occurred during a period of heavy rainfalls in the Bedretto region. Rainfall-driven microearthquake triggering is a plausible but somewhat debated scientific hypothesis, and our observations form an interesting test case for the theory. We are currently collecting regional precipitation and meltwater data, to do an in-depth study, with recently developed microearthquake detection algorithms.
Another clue is that microearthquake sequences are not at all uncommon in underground operations such as the ones performed in the BedrettoLab. Activities like drilling and tunnelling can change crustal stresses and pore pressures in the host rock, even at some distance from the tunnel itself. Such perturbations are also likely candidates to drive the observed microquake activity.
The Bedretto team is currently expanding the seismic monitoring network in order to be able to better characterize the microseismic events, not just in the immediate vicinity of the laboratory, but also across a larger region around it.
The reservoir stimulation activities are completed for the moment, which will allow the reservoir system to equilibrate. With the expanded monitoring network, we will be able to even better study the microseismic activity and hunt for further clues. With the additional knowledge about the background seismicity in Bedretto, the team is preparing next stimulations starting in autumn.
After first stimulations in November 2020, in the next days, Geo-Energie Suisse (GES) will perform another set of high-pressure injections at the BedrettoLab using a multi-packer-system. Packers are large rubber sleeves that are lowered into the borehole to divide it into several sections. They allow to stimulate the different sections separately with exactly the pressure and the amount of water needed. This method aims at enhancing the permeability per section in a controlled way while minimizing induced seismicity. GES conducts the so far largest stimulation test at BedrettoLab as part of the DESTRESS project.
For these stimulation tests, GES will use a set of 14 packers (see illustration showing the concept) that are mounted at fixed intervals of 12 to 25 meters. This means, that a larger rock volume will be stimulated than in November, when the packers were installed at narrower intervals. The packers are placed at depths of about 250 to 400 meters in the borehole ST1, whereby only the lowest sections will be stimulated. The goal is to observe how the packer system behaves as a whole and if the packers succeed in separating the sections allowing targeted stimulations.
As for all activities in the BedrettoLab, safety is the top priority also for these stimulations. For this reason, GES and ETH Zurich closely monitors the preparation and implementation of the stimulations. The chances that these stimulations will cause a felt or even damaging earthquake are very small, about 1 in 10 Million.
After many months of preparations, one of the project partners, GeoEnergie Suisse AG (GES), is now ready to start the first full-scale stimulations in the Bedretto Lab. These stimulations are part of a European Research project DESTRESS that aims at demonstrating so-called soft stimulation techniques for creating a heat exchanger in the underground and extracting geothermal energy.
By injecting a few tens of cubic meter of water into the rock under high pressure, GES aims at creating a network of small fractures that connect the two experimental boreholes. This process triggers very small earthquakes. Eventually, water can then circulate through numerous tiny fractures from one borehole to the other and gradually heat up on its way.
GES has chosen the Bedretto Lab to demonstrate the concept of multi-stage stimulations that they are purposing to use for commercial geothermal plants. To conduct multi-stage stimulations, the borehole is temporarily divided into different sections or stages, which are stimulated separately. GES hopes to have more control on the reservoirs properties by applying this method and to limit the seismic risk.
For all activities in the Bedretto Lab, safety is the top priority. For this reason, ETH Zurich has conducted an extensive seismic risk study to evaluate the chance of damaging earthquakes in consequence of these stimulations. The chance of such earthquakes of magnitude 2 or 2. 5 to occur is estimated to be about 1 in 10 Million. A dense monitoring system has been installed to closely monitor the stimulations. Its data will feed into a set of so-called Traffic Light Systems defining criteria to stop any activity in case certain thresholds are exceeded. They take into account the observed vibrations, the magnitudes of induced events, and the pressure build-up on a nearby fault. One such predefined criteria would be an earthquake of a magnitude of 0.5 or bigger, which would lead to an immediate stop of any ongoing activity.
Besides relying on such predefined thresholds used for classical Traffic Light Systems, a specific goal of the project is to demonstrate and test more sophisticated approaches. To this end, Advanced or Adaptive Traffic Light Systems are implemented taking into account real-time data during the stimulation and assessing whether a stimulation can continue (green), has to be paused (yellow) or must be stopped (red). In addition, we will update the risk assessment after having injected 5m3 of water and decide about the continuation of the stimulations. This process will be repeated after each stimulation of one of the borehole stages. 6 November 2020
Monitoring boreholes were instrumented with geophones, high-frequency accellerometer, piezoelectric In-situ Acoustic Emission (AE) sensors, AE-accelerometer sensor chains, ultrasonic transmitters, Fiber Bragg Grating (FBG) sensors, fibre optic cables, rod system with centralizers, tiltmeters, pore-pressure sensors and mulitpacker. These instruments will monitor the rock volume during fracture generation and water circulation.
Pilot boreholes were drilled to allow a representative characterization of the Bedretto reservoir, to be used as monitoring boreholes for the stimulation and circulation experiments in later phases and to provide sufficient flexibility in hosting the stimulation boreholes.
The tunnel of Bedretto is identified by the ETH Zurich as ideal for experiments in the field of geothermal energy. An agreement for the use of the tunnel is signed with the Matterhorn-Gottard-Bahn and work begins on preparing the laboratory.
The people approve the new Federal Energy Act, which corresponds to the first package of the Energy Strategy 2050. The latter provides that geothermal energy will cover 7% of demand in 2050. Scientific research is needed to increase this percentage!
The Furka base tunnel was opened in April 1982. The transport of cars through the tunnel began in September 1982. The Bedretto Window remains unused and no maintenance is planned in the following years.
The construction of the Furka railway tunnel begins and the tunnel of Bedretto is being built with the goal of speeding up construction work. The possibility of also connecting Ticino to the Furka tunnel has been abandoned.