Induced seismicity in Basel
Deep Heat Mining Basel, also Deep Mining Project is a joint project of Geopower Basel AG and Geothermal Explorers Ltd.. to produce electricity and heat from geothermal energy ( geothermal) by means of deep boreholes in the Basel area. The Basel system is a pilot project under the Swiss Deep Heat Mining Projects. The project was definitely set in 2010.
The proposed system should operate on the principle of a flow heater. A pump forces water initially to produce a system of fissures in the earth's crust ( hot dry rock process or Hot Fractured Rock method ). In the lessons cavities, cold water is pumped, the water heats up and is conveyed back to the surface.
This procedure should come first in Basel commercially used. The water heats up to 200 degrees Celsius and is then pumped back to the surface. A heat exchanger in a closed system which extracts energy for production of electric power with turbine, the rest of the heat is dissipated as district heat. Investment of about 80 million Swiss francs are estimated for the construction of the plant. In addition to the Geopower Basel AG are involved in building the cantons of Basel-Stadt and Basel-Landschaft and various energy providers.
The Basel site was chosen because of the special tectonic position. Basel is located at the southeastern end of the Upper Rhine Graben. This was at a point where raised in front of around 40 million years ago, southern Germany to a large vault and the earth's crust has been stretched. This activity subsided to around 10 million years ago and led to a wide moat and a reduction of several thousand meters between the Vosges and the Black Forest. The strain induced in the rock, a natural circulation of hot pore water body. So, it is already at a depth of five kilometers find rocks that are suitable to 200 degrees Celsius for heat recovery.
In 2005 took a first test drilling at customs Otterbach place with a depth of 2700 m. This hole was the basis for a feasibility study, which is behind the project. The project provides for three test holes with a depth of 2700-5000 meters in the area Kleinhueningen and St. Johann are made in the course of three years. Here, the evidence must be provided that the rock can actually fracturing using pressed- water. By 2009, the corresponding power plant should be built.
-Induced earthquakes ( induced seismicity )
In December 2006 a pilot hole to 5000 m depth was carried out in Kleinhueningen. Thereafter, water was pumped into the rock to fracture the rock, and to increase the permeability. It had been expected that this small earthquakes, so-called micro-earthquakes occur. However, this quake should be able to be recorded by highly sensitive measuring devices, while providing information about the success of the project.
When water injection occurred in December 2006, not only to the expected smaller quakes, but also stronger, more noticeable tremors measuring up to 3.5 ( Local Richter magnitude ). So on the evening of December 8, 2006 an earthquake with a magnitude of 3.4 occurred. Already in the course of the day minor shocks were perceptible. As a result, there were numerous minor earthquake of magnitude 0.5 to 1 and another earthquake of magnitude 3.1 on January 6th 2007, although the water pressure was reduced immediately after the first severe shock in the borehole. The seismic tremors were not yet subsided until February 2007. On January 16 January and 2 February 6, further earthquakes occurred with magnitudes above 3
Major damage was not, however, the population was insecure. The Geopower Basel AG left the rig after the event break down and stopped the project for the time being. The Basel authorities consider the project again, it evolved to a discussion of its continuation.
Experts in geothermal expressed in the newspaper Die Welt that these artificially triggered earthquakes could reduce the risk of new Basel earthquake. According to the Swiss Seismological Service, however, this effect is negligible.
The prosecutor's office in Basel, then against the managing director of Geothermal Explorers Ltd.. Charges levied. Meanwhile, it was decided to discontinue the project, because expectations according to a present risk analysis alone during the plant with another massive earthquake and damage of around CHF 40 million. During operation beyond loss of around six million Swiss francs per year are expected. The court has acquitted the geologist, the criminal proceedings were terminated.