The Future of Geothermal Power
A total of 18 GRC board members and others responded in a timely fashion to Dr. Garg's initial request for input and a follow-up on his draft recommendations report. As may be expected from the diversity of GRC membership, comments covered a wide range of topics. However, several common themes were discerned by Dr. Garg, which formed the basis of a report delivered by GRC president Stuart Johnson (Caithness Operating Co., Reno, Nev.) at a DOE-Industry geothermal program briefing at the Lawrence Berkeley National Laboratory. A synopsis of that report follows.
Exploration of Resource PotentialMany previously explored geothermal prospects remain undeveloped in the United States. To ensure that these prospects will be developed over the near-term, it is necessary to verify their resource potential by drilling and testing cost-shared confirmation wells. There also is a need to identify new prospects if geothermal energy is to continue in the long-term as a significant component of the U.S. energy mix. Specific suggestions include:
- Expanding DOE's GRED (Geothermal Resource Explo-ration and Definition) program.
- Fund cost-shared drilling for reservoir confirmation and new exploration holes, including both thermal gradient and slim holes.
- Develop improved geophysical and geochemical exploration techniques.
Drilling TechnologyDrilling costs represent a major part of total geothermal exploration and reservoir development costs. Reduced drilling costs are essential for reducing the cost of geothermal power. Specific suggestions include:
- Develop improved materials and techniques for controlling lost circulation, which is the biggest problem in geothermal drilling.
- Develop better cements for geothermal applications.
- Develop improved methods of logging drilling and drill bits.
- Reactivate the Geothermal Drilling Organization (GDO) for industry participation.
Reservoir ConfirmationGeothermal power projects typically require detailed analysis of exploration, well drilling and testing data, as well as numerical confirmation of adequate resource supply for 30 years or more.
Increased confidence in reservoir model predictions would ease the project-financing process. In addition, robust reservoir models are needed for rational reservoir management and to avoid costly failures, such as premature breakthrough of cold injected fluids into production zones. Specific suggestions included:
- Develop and demonstrate techniques for combining geophysical (e.g. microgravity, self-potential, MT, CSAMT, seismic) and geochemical (e.g. noble gases, chloride distribution, etc.) data with traditional reservoir engineering data to develop more robust reservoir models.
- Improve numerical reservoir modeling techniques (e.g. incorporation of fluid chemistry and non-conservative tracers).
- Publish case studies to demonstrate the efficacy of reservoir modeling.
Enhanced Geothermal SystemsIn the short term, enhanced geothermal systems (EGS) technology can be used to enhance the life of existing hydrothermal systems. EGS represents a vast geothermal energy resource for the future after conventional hydrothermal fields have been depleted. Specific suggestions included:
- Continuing the cost-shared DOE-Industry projects at a funding level ad-equate for testing several different concepts in the near-term.
- Near-term EGS projects should focus on producing hydrothermal systems.
Hardware RequiredCertain improvements in hardware can lead to reductions in geothermal exploration costs, as well as operations and maintenance costs. Specific suggestions
- Develop new technology for hydrogen sulfide abatement.
- Develop protective coatings to reduce silica and other scaling, as well as corrosion from hydrochloric acid in steam.
- Develop downhole pumps that can withstand temperature up to 400 degrees F.
- Develop new downhole logging tools (e.g. PTS-density tool).
Low-temperature SystemsThe number of high-temperature (greater than 400 degrees F) and medium-temperature (300-400 degrees F) geothermal reservoirs that remain to be developed is limited. However, a large number of lower temperature prospects (212-300 degrees F) are available for potential development. Conversion technology for the medium- and high-temperature geothermal resources is mature. The recommendation here is to develop and demonstrate economic conversion technology for geothermal resources in the low-temperature range.
Basic ResearchThough it is important to support cost-shared geothermal exploration and development projects, it is essential to fund basic research at an appropriate level to provide the necessary scientific/technological underpinnings for more applied work. Specific suggestions included:
- Both non-profit institutions (e.g. universities) and for-profit private companies should be eligible to receive grants/contracts for basic research and development of innovative geothermal technologies. The current trend in DOE budget allocations seems to de-emphasize basic research and preclude private-sector companies from participation.
- Important research areas include the need for development of improved geophysical and geochemical exploration techniques; better methods of detecting and characterizing fracture permeability; and improved reservoir modeling techniques.
Information DisseminationDissemination of research and development (R&D) results, education and public outreach are essential components of a publicly funded geothermal R&D program. Specific suggestions included:
- Continue the funding of scientific/technical meetings and publications to ensure timely dissemination of R&D results.
- Continue and expand public information efforts on the benefits of geothermal energy as an indigenous energy source that can reduce greenhouse gas emissions and enhance national energy security. Such efforts are essential to public perception of geothermal energy as a viable renewable energy source for the future.
Distributed PowerFunding is needed to promote off-grid geothermal power systems and non-electrical uses of geothermal energy. Specific suggestions included promotion of:
- Off-grid village power including small-scale (50 kilowatt to 5 megawatt) power generation.
- Minerals recovery from geothermal brines.
- Agribusiness and other direct uses (e.g. space heating) of geothermal energy resources.
Sidebar:To assist the U.S. Department of Energy prioritize its future research and development activities, the Geothermal Energy Association canvassed its members and associates to ask their opinions on what should be the agency's foremost geothermal research and development priorities. With rankings from 1 through 7 (with 1 being the lowest rank), respondents placed the average priority of various research and development categories as follows:
Geothermal R&D Survey Results
Rank Research Category
5.5 Cost-shared drilling
5.2 Enhanced geothermal systems
5.1 Reservoir engineering
5.0 Exploration technology
5.0 Fracture research
5.0 Low-temperature power production
4.7 Drilling technology
4.7 Conceptual modeling
4.7 Injection technology
4.3 Higher-temperature power production
4.3 U.S. Geological Survey resources
4.0 Advanced production logging
4.0 Tracer research
3.9 Scale mitigation
3.8 By-product research
3.7 Case studies
3.7 Downhole pumps
3.7 Well logging
3.4 Direct use
3.3 Hydrogen production
2.6 Geopressured research
2.4 Magma research