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Geothermal Energy Resource Exploration and Drilling: Resource Requirements and Impact Sources

The development potential of a geothermal reservoir is evaluated by various studies, surveys, and drilling activities.

Before geothermal resources can be developed, various exploratory and drilling 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. Once data and surveys have been compiled and analyzed, more invasive activities like geophysical testing, drilling temperature gradient wells, drilling holes for explosive charges for seismic exploration, and core drilling take place. If the site is viable for development, additional drilling and testing of exploration wells is conducted to more fully characterize the geothermal reservoir. This involves flow testing of wells, producing geothermal fluids for chemical evaluation, and injecting fluids into a geothermal reservoir.

The following factors could contribute to adverse environmental impacts during the resource exploration and drilling phase of project development.

Resource Exploration and Drilling Phase — Requirements and Impact Sources

  • Acreage Requirements — Acreage requirements for the resource exploration and drilling phase depend on the geometry of the geothermal system being investigated and the anticipated size of the power development, but usually range from about 2 to 7 acres during the initial exploratory activities. Acreage requirements expand to 5 to 50 acres with the drilling and installation of flow testing wells and construction or improvement of access roads.
  • Emissions — Emissions would be limited to those created by vehicles and drill rigs. Dust emissions caused by vehicle traffic would also occur. A diesel generator may be used at the site to power equipment. As wells are completed, well venting could result in emissions of hydrogen sulfide, carbon dioxide, mercury, arsenic, and boron (if present in the geothermal resource).
  • Waste Generation — Wastes would be limited to those generated by exploration crews. Drilling wastes would be generated, but collected and transported to licensed off-site locations for disposal. During well testing, excess geothermal fluids would be stored in temporary pits or sumps (generally lined with plastic or clay); after the water evaporates, the remaining sludge would be removed and disposed of off-site.
  • Water Needs — Water needs would be negligible. Water would be used for controlling fugitive dust, making concrete, and supplying potable water for the drilling crew. Any water that might be required for drilling likely would be either trucked to the site or obtained from an on-site or near-site source (e.g., on-site well or municipal water supply).
  • Workforce — Only a small crew would be needed to conduct various studies and surveys and the initial well drilling. Once the drilling and testing of exploration wells begins, a workforce size of 10 to 15 people would be on-site at all times, with more workers coming and going periodically with equipment and supplies (with 15 to 20 trips to mobilize and demobilize the drill rig and 10 to 40 daily trips for commuting and hauling in equipment). Typically, none of the workforce would reside on-site, but minimal support facilities might be required for weather contingencies. Several hundred workers would be required to construct pipelines; transmission line construction could require a workforce of about 20 to 100 individuals, depending on the line length.
  • Time and Materials — It would take no more than a few days to conduct seismic surveys. The initial drilling could last for several weeks. Materials required are related mainly to well drilling and would be brought to the site by truck. In total, exploration and drilling activities could take between one and five years to complete.
  • Utility Requirements — There would be no utility requirements during the initial exploration activities; drill rigs would be operated by diesel engines. Any electrical power needs would be met through use of portable generators.