GEISER

Geothermal Engineering Integrating Mitigation of Induced Seismicity in Reservoirs

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 Obiettivo del progetto (Objective)

'The project contributes to the improvement of the concept of Enhanced Geothermal Systems by investigating the role of induced seismicity, which is twofold: (i) an instrument to image fluid pathways induced by hydraulic stimulation treatments, which has been done to some extent in previous projects; and (ii) an implication of such treatments to potential seismic hazards. The mitigation of induced seismicity to an acceptable level is the major intent of this project. For this purpose, we set as our goals (1) to understand why seismicity is induced in some cases but not in others; (2) to determine the potential hazards depending on geological setting and geographical location; (3) to work out licensing and monitoring guidelines for local authorities, which should include a definition of what level of ground motion is acceptable; and (4) to develop strategies to fulfil the task of the stimulation and improve the hydraulic properties of the geothermal reservoir without producing large magnitude events. To accomplish the project goals a high quality database of case studies will be assembled. This will include data on seismicity and ground motion, geomechanics, reservoir characteristics, injection/production, and surface deformation, as well as information on the local stress field and local geology. The interpretation will be based on data from the sites: Soultz-sous-forêts (France), Basel (Switzerland), Groß Schönebeck (Germany), KTB (Germany), Larderello/Latera (Italy), Campi Flegrei (Italy), Hengill, Krafla, Reykjanes (Iceland), Groningen (Netherlands), and others (Berlin, El Salvador; The Geysers, USA). The GEISER-project will overcome shortcomings of previous work by including model based forecast of stimulation and/or production induced seismicity. Developing soft stimulation strategies and guidelines on how to react on induced seismicity will support the acceptance of geothermal applications.'

Introduzione (Teaser)

Injecting high-pressure water into the Earth and recovering the heat from the water returning to the surface could provide clean, renewable electricity. EU-funded scientists have developed a risk assessment framework to increase implementation.

Descrizione progetto (Article)

Until recently, geothermal power technology exploited heat that was deep in the ground in areas with sufficient water and rock permeability for easy energy extraction. Thanks to so-called hydraulic pumping, enhanced geothermal systems (EGSs) can now be implemented in areas previously not suited to recovery of ground heat.

Hydraulic pumping involves injecting high-pressure water into the rock, creating a subsurface fracture system that enhances permeability. The freed water then travels through the rock, absorbs heat and is returned to the surface as in naturally occurring hydrothermal systems. The heat energy can be converted to electricity and the now cooled water pumped into the Earth again, creating a closed, sustainable and efficient loop.

One of the potential difficulties with EGSs is induced seismic activity. European scientists investigated methods to mitigate that seismic activity with EU funding of the 'Geothermal engineering integrating mitigation of induced seismicity in reservoirs' (http://www.geiser-fp7.eu (GEISER)) project.

Methods to image fluid flow paths induced by hydraulic stimulation were employed. Scientist studied past stimulation experiments as well as two sites of on-going activity. Data revealed that the largest seismic events often occurred in the hours and days after termination of injection. Many projects showed a relationship between injected energy and seismic energy, pointing the way to mitigation strategies including 'soft stimulation' approaches. In addition, in many cases seismic activity was less in sedimentary rock than at sites that access reservoirs.

For the first time, ground motion prediction equations are available that are specifically for geothermal sites. The team also developed a comprehensive framework for assessment of seismic hazard and risk associated with EGSs. It can be used throughout exploration and production to warn of danger and enable mitigation of undesired effects during operation.A cost-benefit analysis covering exploration and production will enable all stakeholders to evaluate interests and risks accurately. Scientist have developed a recommended strategy to enhance public support of EGS. This should advance exploitation of this renewable, emission-free source of electricity.