US-Japan Bilateral Enhanced Geothermal systems Project
Andrew Coleman, EPRI, Phone +1650-855-8971, E-mail:
Gene Suemnicht, EGS, Phone +1 707-595-8761, E-mail:
Overview
Japan is beginning to revive its geothermal resource base after the shutdown of nuclear plants in 2011 following the Tőhuku earthquake and tsunami. Emphasizing geothermal production will enhance baseloads typically supplied by other dependable sources of electricity but carbon-intensive sources such as coal, oil and liquefied natural gas. With Japan’s attempts at rebalancing its power sources, more focus was attached to renewable resources such as geothermal energy. New plans in Japan may strike a reasonable mix of energy sources to reduce future supply risks while reducing greenhouse gas emissions. Geothermal economics continue to show greater benefits when included in a balanced energy portfolio. Technologies developed in enhanced or engineered geothermal system (EGS) research will help future developers reduce drilling costs and potentially utilize marginal portions of existing geothermal systems. Japanese EGS experiments since 2011 attempted to hydraulically stimulate and connect fracture systems in relatively impermeable rocks to either resurrect hot but impermeable portions of existing developed fields or lay out the framework for discovering or developing new sites. Japan has about 20GW of geothermal potential. Japan has developed only about 2-3% of its geothermal potential and remains a longer term investment in clean energy resources.
Methods
EGS experiments by Calpine Corporation in the northwest part of Geysers field were originally based on the successful low-volume and low-pressure injection experiments at Hijiori. Japan. The EGS experiments at Hijiori and Ogachi showed that it is possible to map microearthquake hypocenters induced by stimulation and then drill into the hypocentral cloud, rather than drill two or more wells and attempt to connect them with fractures. Both experiments demonstrated that understanding the natural fracture system and the local/regional stress field helped manage the drilling practices more effectively and efficiently.
Results
Phase I of this bilateral information exchange reviewed injection and stimulation practices at The Geysers., Enhanced water injection has been crucial in sustaining productivity at The Geysers since the late 1990s. EGS experiments in the northwest Geysers were funded by the US DOE and have shown the potential of developing a very high temperature portion of the field.
Phase II of the bilateral information exchange reviewed current seismic monitoring methods to identify technical gaps and outline lessons learned from methodologies typically deployed at EGS project sites. The study included an evaluation of how microseismic data have been used to track and/or target fractured rock volumes at geothermal sites in the United States and Japan—with potential applications to the Fukushima Prefecture, Japan.
Conclusions
Ensuring on-target drilling operations is one of the main economic considerations in geothermal exploration and development. In Japan many high potential geothermal prospects occur in national park systems. Seismicity in developed geothermal systems and in EGS stimulation experiments has become an environmental concern because of felt earthquakes in surrounding communities. Seismicity within all geothermal systems generally occurs at very low levels and felt events (M > 3) are the exception rather than the rule. While sustaining operations in or around sensitive national parks might sound daunting, studies carried out to improve EGS potential and seismic monitoring bring more assurance to projects in environmentally sensitive locations. Siting remains a key consideration even with the strong considerations for clean energy; however, through modeling and using practical injection and stimulation practices the drilling footprint may be reduced which can significantly lower capex costs. Japan is actively evaluating ~ 20 sites for potential development. Robust seismic monitoring systemswill be important as these projects move forward.
References
Coleman, A. (Ed.). 2014 United States – Japan Bilateral Enhanced Geothermal Project Phase I Review of Injection, Monitoring, and Stimulation at The Geysers Geothermal Field. Report ID 3002004577
Coleman, A. (Ed.) 2015 Unted States – Japan Bilateral Enhanced Geothermal Project Phase II Review of Seismic Monitoring Practices at They Geysers Geothermal Field, CA and the Hijiori and Ogachi Fields, Japan. Report ID 3002005464
Geothermal Resources Council (GRC), 2010, Special Report 20, The Geysers Geothermal Field, Update 1990-2010, p. 44
Kaieda, H. 2014, Hijiori HDR Reservoir Evaluation by Micro-earthquake Observation, Geothermal Resources Council Transactions, 38, 295-299.
MIT (Massachusetts Institute of Technology), 2006. The Future of Geothermal Energy: Impact of Enhanced Geothermal Systems (EGS) on the United States in the 21st Century. Boston, MA: MIT Press