Geothermal Engineering Integrating Mitigation of Induced SEismicity in Reservoirs

Kristján ÁgústssonÓlafur Flóvenz, Egill Á. Guðnason

The GEISER project started at the beginning of the year 2010. It was funded by the European Commission. ÍSOR’s participation was supported by GEORG. The specific objectives of GEISER were:  

to understand why seismicity is induced in some cases but not in others

to assess the probability of seismic hazards depending on geological setting and geographical location

to propose licensing and monitoring guidelines for local authorities, including a definition of acceptable ground motion levels

to investigate strategies for ‘soft stimulation’ that sufficiently improve the geothermal reservoir’s hydraulic properties without producing earthquakes that could be felt or cause damage

Guidelines – best practice

• IEA – GIA (International Energy Agency –Geothermal Implementing Agreement)

• IPGT (International Partnership for Geothermal Technology)

• Department of energy, USA• and more

To address these objectives, four main topics were identified:

• Analysis of induced seismicity• Understanding the geomechanics and processes• Consequences of induced seismicity - hazard, risk• Strategies for the mitigation of induced seismicity

WP1: Project Management. GFZ.WP2: Compilation of induced seismicity data and literature from geothermal sites and selection of sites for detailed study. ISOR.WP3: Analysis of Induced Seismicity. GFZ.WP4: Understanding the Geomechanical Causes and Processes of Induced Seismicity. BRGM.WP5: Seismic Hazard Assessment. ETHZ. WP6: Strategies for EGS operations with respect to Induced Seismicity (Mitigation). TNO. WP7: Dissemination. BRGM. 

Icelandic interests

• To study seismicity in Icelandic geothermal systems, particularly induced seismicity

• Geiser: to propose licensing and monitoring guidelines for local authorities– These guidelines could become a recommendation from the

Europian Commission– It was considered important that Iceland would take care of its

special interests in this respect due to different circumstances in utilisation compared to EGS

• At the time of the start of GEISER induced seismicity was not considered an issue in Iceland

Special Icelandic cicumstances

• Geothermal utilization in Iceland is until now from natural geothermal reservoirs– GEISER focused on enhanced geothermal systems – EGS-systems

• Geothermal fields in Iceland are in tectonically active areas and the permeability is mostly fissure and fracture permeability formed in earthquakes

• It was assumed that possible induced activity would not change the character of the natural seismic release significantly

Examples of induced seismicity• Gráuhnjúkar, Hengill, SW Iceland• Húsmúli, Hengill, SW Iceland• IDDP-1, Krafla, N Iceland

The first quakes occurred close to the bottom of the well.

Then they migrated laterally away from it, probably along the top of the molten zone.

Finally the activity was mostly along an inclined plane.

Earthquakes during injection into the bottom feed zone of the IDDP-1

well, Krafla.

HE-8

HE-10

HE-12/15HE-5

HE-7 HE-57

HE-16HE-13 HE-29

HE-19

HE-35

HE-30

HE-41/43/45/47

HE-40 HE-52HE-42/44/46

HN-4

HN-3

HN-2 HN-6

HN-5/7

HN-10

HN-8

HN-17

HN-12

HN-11HN-9 HN-15

HN-14

HN-13

HN-16

Data from the Icelandic Meteorological Office

Remarks / Iceland

• Wellhead pressure is low and the earthquakes are triggered by increased pressure or caused by thermoelastic process

• In high temperature areas which are located in volcanic centres the events are small indicating weak crust

• Areas in and around shear zones of the plate boundaries are able to produce large events but the activity decreases rapidly with continued injection (Húsmúli)

Húsmúli – change of attitude

• A full-scale injection at Húsmúli in Sept 2011 with a rate of more than 500 L/s caused seismicity that was felt in neighboring communities and it changed the general public attitude

Results - recommendations

• Reykjavík Energy, that operated the field put together a group of specialists, including participants from GEISER. It analyzed the process and recommended the best practices based on the work in the GEISER project

• These recommendations were used by the National Energy Authority, in cooperation with the power companies, to compile regulations and recomendations for reseach- and operation permits for geothermal power plants in Iceland.

Other benefits of GEISER for Iceland

• General knowledge was gained about induced seismic activity

• New methods and monitoring• Warning systems (traffic light), e.g. now in

use during drilling of the IDDP-2 well (DEEPEGS)

Thank you