So far the stimulation has proceeded in line with the plans and the flow of the water, deep down in the deep bedrock has been as expected. As the next step, the analysis of the results will start, which will take about 5 – 7 months.
What is water stimulation and why is it needed?
A key stage in the geothermal project is water stimulation, where water is pumped into a 6.4 km deep borehole, already existing. The stimulus-induced seismic events and the generated water-flow in the deep bedrock are monitored carefully with the monitoring network. This is how the place for the end of the other borehole will be determined.
The authorities monitor the project, the monitoring network covers the metropolitan area
The exact timings for seismic events induced by water stimulation can’t be estimated and and therefore they do not occur regularly at certain times. Some of them make noise. Sound waves can also resonate eg. in windows and structures. The structure of the rock determines to which areas the sounds are transmitted at any given time. The underground geophonic network is used to monitor the flow of water in the rock and to keep the micro events within the boundaries of the authorities. In addition, the surface acceleration sensors installed in the surrounding area measure how the events are felt on the surface of the ground. The Institute of Seismology at the University of Helsinki, responsible for project control, monitors the project with its own meters and also has access to the data of the St1 measurement network in real time. On the basis of the resident observations we have received, we have also increased acoustic measuring instruments for areas where observations have become more recent. We will, for example, with the hydrophone installed at the bottom of Laajalahti, explore the transmission of sound through water.
We will implement the stimulation according to the measures required by the authorities and report all the events of 1.2 magnitudes or more on the project website, in accordance with the plan agreed with the authorities. Up to now, over 6 weeks, there have been 27 reported events, of which 6 unfortunately happened at night. These events have been noticeable in nearby areas on the surface of the earth, for example, as thunders or bangs. All micro-events have been within the limits set by the authorities, which are set for the project considerably lower than those allowed for example in blasting operations. Sounds and micro events in bedrock do not affect ground or near underground structures. Residents from some houses have reported vibration. Sense of vibration can be caused e.g. in some older houses the way in which the foundation of the house is made, if the foundation does not have sufficient attenuation layer. Even then, any possible movement in the structures is significantly below the limits of the blasting operations and is not so big that it would cause damage.
The project's stimulation test phase will take few days, during which voices can be heard in the region. We apologize for the inconvenience we cause and we ask patience for a while. The completed geothermal plant does not have sounds.
Emissions free geothermal energy is new in Finland, elsewhere in use
Otaniemi's geothermal heat construction site is Finland's first geothermal deep-heat pilot project. Based on the feedback we received during the stimulation phase, the project has been primarily taken with interest and we have received valuable notifications from the locals for the perceptions of micro events that we have been able to compare to the measurement data. Some feedback has also emerged from the disturbance of seismic events and sound waves in the water simulation phase that we have taken into account in strengthening the measurement network.
Geothermal heat plants are in use, for example, in France, the United States and Germany and more are being planned. Thanks to its favorable geological location, Iceland has for many years produced all the heat it needs and half its electricity with geothermal energy. Compared to other geothermal countries, drilling at several kilometers of depth in Finland's hard granite bedrock and achieving water flow at a sufficient depth is one of the biggest challenges of the project. The analysis following the stimulation stage will determine the continuation of the project. The planned facility in Otaniemi could cover up to 10% of Espoo's district heating needs with emission free energy.
Follow the project, ask, give feedback
Geophone measurement results as well as up to date information can be monitored online www.st1.eu/geothermal-heat
All seismic events in Finland and adjacent areas can be monitored at the Institute of Seismology www.seismo.helsinki.fi/bulletin/list/alert/current_map.html
If you have made earthquake observations yourself, you can report them to Institute of Seismology using the observation form: https://elomake.helsinki.fi/lomakkeet/89816/lomake.html