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Geothermal Energy Project Phases and Activities

Impacts from a geothermal energy project can result from activities that occur during each phase of the project: resource exploration and drilling, construction, operations and maintenance, and decommissioning and site reclamation.

What Activities Occur During the Resource Exploration and Drilling Phase?

Before geothermal resources can be developed, various exploratory activities must take place. Exploration begins with the gathering of data and detailed surveys to locate higher temperature gradients and to characterize the development potential of a geothermal reservoir. The kinds of surveys and studies required include:

  • Satellite imagery and aerial photography;
  • Volcanology studies;
  • Geologic and structural mapping;
  • Geochemical surveys;
  • Geophysical surveys; and
  • Electrical, magnetic, chemical, seismic, and rock studies.

Once data and surveys have been compiled and analyzed, more invasive activities like geophysical testing, drilling temperature gradient wells (above the reservoir), drilling holes for explosive charges for seismic exploration, and core drilling take place. Specific activities affecting the project site include: clearing of vegetation and building of roads to increase access to the project site, detonating small charges below the ground surface to create seismic pulses for the seismic surveys, burying cables and sensors as part of the seismic surveys, drilling of wells (typically with truck-mounted rigs), and earth-moving activities to prepare the drilling site. During the exploration and drilling phase, fluids produced during drilling (e.g., drilling mud and groundwater) would be collected by sump or tanker truck and transported to licensed off-site locations for disposal. The exploration and drilling phase generally takes between one and five years to complete.

If a site is confirmed as a viable prospect for geothermal development, exploration wells are drilled to test the reservoir. Activities include flow testing of wells, producing geothermal fluids for chemical evaluation, and injecting fluids into a geothermal reservoir. Sumps or pits to hold excess geothermal fluids would also be constructed. Water would be left to evaporate, but remaining sludge would be removed and transported to licensed off-site locations for disposal. Some infrastructure construction may also be required. If a reservoir and geothermal well are determined to be sufficient for development, a wellhead with valves and control equipment are installed on top of the well casing.

What Activities Occur During the Construction Phase?

After the exploration and drilling phase, the project site is prepared for production. The construction phase involves the construction of the geothermal field(s), infrastructure, power plants, and transmission lines. Activities in this phase of development would include:

  • Clearing, grading, and constructing access roads;
  • Clearing, grading, and constructing electrical generation facilities;
  • Building facility structures;
  • Drilling and developing well fields;
  • Installing pipeline systems; and
  • Installing meters, substations, and transmission lines.

The construction phase of the development process would result in the greatest area of land disturbance at the geothermal energy project site, although some of the disturbed land would be reclaimed once construction activities end.

What Activities Occur During the Operations and Maintenance Phase?

The operations and maintenance phase involves the operation and maintenance of the geothermal field(s) and the generation of electricity. The types of operations and maintenance activities depend on the size and temperature of the geothermal reservoir. Typically, only high-temperature reservoirs are suitable for the utility-scale production of electricity, although new technologies are proving that lower-temperature water can also be used for commercial purposes. The operations and maintenance phase can last from 10 to 50 years.

What Activities Occur During the Decommissioning and Site Reclamation Phase?

Once geothermal production ceases, the production wells are abandoned, facility structures and infrastructure are removed, and all the disturbed areas at the project site are reclaimed. Well abandonment involves plugging, capping, and reclaiming the well site. Reclamation includes removing the power plant and all surface equipment and structures, regrading the site and access roads to preproduction contours, and replanting vegetation to facilitate natural restoration.