Project GeoBest

Summary

The Swiss Seismological Service (SED) is implementing the GeoBest project on behalf of the Swiss Federal Office for Energy (SFOE) to provide cantonal and federal authorities with guidelines on how to handle seismic hazard in the framework of the environmental risk assessment. Within GEOBEST, selected pilot projects in Switzerland will be supported in the necessary seismic monitoring of natural and induced seismicity. GeoBest supports the pilot project in the first two years, that are most critical with respect to the financial risk, by providing seismological instrumentation from the GeoBest instrument pool and partial financial support for the installation and operation of the seismic monitoring network. In return the pilot projects grant SED access to project data needed for seismic hazard assessment and the development of best practice guidelines.

Background

(Text based on: Kraft at al., 2010)

With the global challenge to satisfy an increasing demand for energy while at the same time stabilizing or reducing carbon dioxide (CO₂) concentrations in the atmosphere, deep geothermal resources are being increasingly recognized by society as an attractive alternative energy source. Deep hydrothermal resources, such as aquifers at depths larger than 2km with sufficiently high productivity, have been successfully exploited for many years, but their distribution and potential for supplying electricity is limited. However, artificially created Enhanced or Engineered Geothermal Systems (EGSs) do not suffer this restriction.

In general, deep geothermal resources are exploited by circulating fluids through a geothermal reservoir using a number of deep injection and production wells, thereby extracting heat from the permeable or fractured rock mass. This operation invariably alters the stress and pore pressure in the subsurface. The changes tend to be most pronounced during the EGS reservoir creation (i.e. stimulation) phase, but they also occur in the operational phase of EGS and deep hydrothermal systems (Giardini, 2009).

It has been realized over the last 20 years, that the Earth's crust generally supports high shear stress levels and is often close to failure. Thus, even small changes of the stress and pore pressure in the subsurface due to Earth engineering endeavors or even anomalously heavy rainfall can be sufficient to induce seismicity in natural systems (e.g., Hainzl et al. 2006, Husen et al. 2007). Historically, the most damaging events, are associated with the impoundment of reservoirs (Gupta, 1992). However, earthquakes of sufficient size to cause damage to localities have also been associated with mining activity (Gibowicz, 1990), long-term fluid withdrawal wells (Segall, 1989), and long-term fluid injection wells (Nicholson and Wesson, 1990; Evans et al. 2011).

Even though, massive stimulation injections have routinely been performed at EGS sites since the early 70s, the issue of the seismic hazard associated with these operations has only recently come to the fore. This is because the pioneering EGS developments at Fenton Hill (USA), Rosemanowes (UK), Hijiori (JP) and Soultz (F, 3.5 km reservoir) did not produce events large enough to disturb the local population. Recent attempts to develop EGS at 4.5-5.0 km at Soultz (F), Cooper Basin (AUS) and Basel (CH), and deep (~3km) hydrothermal systems in Landau (D) and Unterhaching (D) produced events approaching or exceeding magnitude ML=3. A recent review of induced seismicity associated with deep fluid injections in Europe, including recapitulatory case histories, is given by Evans et al. (2011).

The processes and conditions underpinning induced seismicity associated with deep geothermal operations are still not sufficiently well understood to make useful predictions as to the likely seismic response to reservoir development and exploitation. The empirical data include only a handful of well-monitored EGS experiments; models are consequently poorly constrained. Unfortunately, datasets of well-monitored deep hydrothermal experiments are missing and empirical constraints of induced seismicity models for these cases do not exist. Given that the majority of the projects underway or planned in Europe are of the hydrothermal type, there is hope that this deficit can be remedied in the near future through a close cooperation of geothermal industry, science and public authorities. 

This is where the GeoBest project comes to play. By supporting selected pilot project for a limited time, SED facilitates the dialog with geothermal industry. Besides of the unique opportunity to collect high quality seismic data and being able to access relevant project data,  gaining first hand practical experience in this field is of paramour importance for the development of significant best practice guidlines.

Project Description

A detailed description of the goals of the GeoBest projects can be found in the document (pdf).

References:

Evans, K.F., A. Zappone, T. Kraft, N. Deichmann and F. Moia (2011). A Survey o induced seismic response to fluid injection in geothermal and CO₂ reservoirs in Europe, accepted for publication in Geothermics.

Giardini, D. (2009),  Geothermal quake risks must be faced, Nature, 461,  pp. 848-849.

Gibowicz, S.J. (1990). Seismicity induced by mining. Advances in Geophysics, 32, pp. 1-74.

Gupta, H.K. (1992). Reservoir-induced Earthquakes. Elsevier, Amsterdam, 364 pp.

Hainzl, S., T. Kraft, J. Wassermann, and H. Igel (2006). Evidence for rain-triggered earthquake activity, Geophys. Res. Lett., 33, L19303, .http://dx.doi.org/10.1029/2006GL027642.

Husen, S., C. Bachmann, and D. Giardini (2007). Locally triggered seismicity in the central Swiss Alps following the large rainfall event of August 2005. Geophys. J. Int., 171, pp.1126-1134.

Kraft,T., K.F. Evans, D. Giardini, N. Deichmann, and S. Wiemer (2010). Induced seismicity associated with the exploitation of deep geothermal resources, European Geologist, 29, pp.19-20.

Nicholson, C. and R.L. Wesson, 1990. Earthquake hazard associated with deep well injection. US Geological Survey Bulletin 1951, 74 pp.

Segall, P. (1989). Earthquakes triggered by fluid extraction. Geology, 17/10. pp. 942-946.