Environmental Impacts of
Geothermal Energy Development

Operating Agent:
GNS Science
New Zealand

Task Leader:
Chris Bromley
GNS Science
Wairakei Research Centre
Private Bag 2000
Taupo
New Zealand
Telephone: + 64-7-374-8211
Fax: + 64-7-374-8199
E-mail: c.bromley@gns.cri.nz

Participants:

The EC, Iceland, Italy, Japan, Mexico, New Zealand, Switzerland, USA

Description:

Environmental effects of energy use are a worldwide concern. Geothermal is generally regarded as a benign energy source. There are, however, some environmental problems associated with its utilization. To further the use of geothermal energy, possible environmental effects need to be clearly identified, and countermeasures devised and adopted to avoid or minimize their impact. Annex 1 of the GIA was set up to address these issues.

The goals of Annex I are:

• To encourage the sustainable development of geothermal energy resources in an economic and environmentally responsible manner

• To quantify any adverse or beneficial impacts that geothermal energy development may have on the environment

• To identify ways of avoiding, remedying or mitigating such adverse effects

The term “development” here is used in a broad sense to encompass not only energy production but also use for social and economic purposes such as tourism.

The specific objectives of Annex I are:

• To study the effects that existing geothermal developments have had on the environment and determine their cause

• To identify the most likely and serious adverse effects that geothermal developments can have on the environment

• To identify the development technologies that have proven to be environmentally sound

• To publish the results of the studies in international journals and present the results at international forums

• To improve communications between individuals and organizations in different countries, and between different professional groups involved in geothermal development by involvement in collective presentation of the results in international forums

Annex I has been a part of the GIA since its inception in 1997, and in 2005 the Annex was extended through 2009.

Annex I activities are divided into five Tasks.

Task A- Impacts on Natural Features (Subtask Leader: Chris Bromley, GNS Science, Wairakei, New Zealand)

This task focuses on documenting known impacts of geothermal developments on natural geothermal features such as geysers, hot springs and silica terraces. The aim of this task is to provide a sound historical and international basis on which to devise methods to avoid or mitigate the impacts of development on these geothermal features, which often have significant cultural and economic value.

Task B- Discharge and Reinjection Problems (Task Leader: Trevor Hunt, GNS Science, Wairakei, New Zealand)

Work in this Task is focused on evaluating the effectiveness of methods (countermeasures) currently used to mitigate adverse environmental effects of geothermal projects, and shall develop recommendations for improved mitigation methods which are less costly and enhance environmental benefits.

Projects examine the problems associated with disposal of waste geothermal fluids from existing geothermal developments; the effects of CO2, Hg and H2S gas emissions ; and the effects, causes and possible remedies for subsidence.

Task C- Methods of Impact Mitigation and Environmental Manual (Task Leader: Chris Bromley, GNS Science, Wairakei, New Zealand)

The objective of this Task is to contribute to the future of geothermal energy development by developing an effective, standard environmental analysis process. Field management strategies that result in improved environmental outcomes will be identified and promoted based on operational experience. Successful mitigation schemes that provide developers and regulators with options for compensating unavoidable effects are also being identified, documented and promoted.

Task D- Seismic Risk From Fluid Injection Into Enhanced Geothermal Systems (Task Leaders: Ernie Majer, Lawrence Berkeley National Laboratory (acting for Allan Jelacic, DOE, USA) and Roy Baria, MilTech UK Ltd.)

The objective of this Task is to address the issue of the occurrence of significant induced seismic events in conjunction with EGS reservoir development or subsequent extraction of heat from underground.  These events have been large enough to be felt by populations living in the vicinity of current geothermal development sites.  The objective is to investigate these events to obtain a better understanding of why they occur so that they can either be avoided or mitigated.   Understanding requires considerable effort to assess and generate an appropriate source parameter model, testing of the model, and then calculating the source parameters in relation to the hydraulic injection history, stress field and the geological background.  An interaction between stress modeling, rock mechanics and source parameter calculation is essential. Once the mechanism of the events is understood, the injection process, the creation of an engineered geothermal reservoir, or the extraction of heat over a prolonged period may need to be modified to reduce or eliminate the occurrence of large events.

Task E- Sustainable Utilization Strategies (Task Leader: Gudni Axelsson, ISOR- Iceland Geosurvey, Reykjavik, Iceland)

The objective of this Task is to c ollate case histories of models of geothermal developments to see what strategies have worked. Undertake modelling of long term reservoir behaviour to select optimum future strategies given different recharge and resource size scenarios.  Compare environmental gains with economic gains from different sustainable development scenarios. Compare different conceptual and hypothetical reservoir model predictions. Investigate (with agreed scenarios) long term reservoir behaviour, recharge factors, recovery times, and optimised cyclic or staged operation strategies.

Highlights and Outputs of Annex I