Geothermal Engineering Integrating Mitigation of Induced Seismicity in Reservoirs

Induced seismic events during hydraulic stimulation of volcanics at the drill site GtGrSk4 in Groß Schönebeck (modified from Kwiatek et al., Acta Geophysica 2010)

The project GEISER (Geothermal Engineering Integrated Mitigation of Induced Seismicity in Geothermal Reservoirs)  which is co-funded by the European Commission is coordinated by the International Centre for Geothermal Research within the GFZ.

The aim of the project is to contribute to the improvement of the concept of Enhanced Geothermal Systems by addressing the need to investigate the role of induced seismicity (IS), which is twofold:  

• as an instrument to image fluid pathways induced by hydraulic stimulation treatments, which has been done to some extent in previous projects; and
• as an implication of such treatments to potential seismic hazards.

The mitigation of IS to an acceptable level is the major intent of participants. For this purpose, the defined project goals are:  

• to understand why seismicity is induced in some cases but not in others
• to determine the potential hazards depending on geological setting and geographical location
• to work out licensing and monitoring guidelines for local authorities, which should include a definition of what level of ground motion is acceptable and
• to develop strategies to fulfil the task of the stimulation and improve the hydraulic properties of the geothermal reservoir without producing larger earthquakes that pose a threat to buildings and disturb the public.

To address these objectives, four main topics are identified:  

1. Analysis of induced seismicity from representative reservoirs throughout Europe, with input from experts and data from regions outside Europe (Berlín, El Salvador; The Geysers, USA, Bouillante, French Antilles). Induced seismic activity will be analysed in space and time and its relationship with injection parameters, the local stress field and the geological setting will be investigated. These datasets will be compared with other project data, where injection did not cause significant seismicity.
2. Understanding the geomechanics and processes involved in induced seismicity. The influence of factors such as temperature, poroelasticity, fluid injection rate, existing fault segments and time dependent effects will be investigated to constrain the possible mechanisms involved during fluid injection using various modelling approaches as well as laboratory experiments.
3. Consequences of induced seismicity will be addressed by providing an assessment of the seismic hazard presented by events triggered through human activity in comparison to natural seismicity. Results from (1) and (2) will be used to quantify the probability of triggering larger seismic events and to define the potential damage caused by ground shaking. This activity will result in guidelines for licensing and site development for local authorities and industry.
4. Strategies for the mitigation of induced seismicity. On the basis of the recommendations formulated in (3) and of the results of (1) and (2) strategies for “soft injection” will be proposed. The optimisation of a monitoring network and a real-time monitoring system will be presented to help authorities and operators minimize the seismic hazard and manage the risks during operations and production. Experience of past seismic events caused by mining and in the oil and gas industry will be included to address the proper handling of public awareness and acceptance.