Geothermal Exploratory Drilling, Surprise Valley

The Surprise Valley geothermal system in Cedarville (Modoc County) remains largely undeveloped but holds great potential for electrical energy production and direct use, given what is known about the resource. The California Energy Commission (CEC) funded this grant agreement to investigate the temperature and permeability of a deeper resource for energy production on the east side of the valley. Study methods included drilling an exploratory well to a targeted depth of 4,000 feet, mud logging, borehole geophysical logging, well testing, geochemical sampling, and reservoir modeling.

The research team initiated drilling May 15, 2019, and completed on June 8, 2019. The well, Warner Mountain Energy-Exploratory 1 (WME-E1), was drilled to a depth of 3,605 feet. WME-E1 is completed with 7” liner from 0-2,325 feet and 5” liner from 2,276 feet to 3,605 feet with 329 feet of perforated 5” liner placed in producing zones.

Reservoir testing and modeling show that WME-E1 can sustain the maximum artesian flow over 20 years or more. With additional production and injection wells, the Surprise Valley geothermal reservoir can sustainably support much higher levels of production. The productivity index of WME-E1 is among the highest level seen in the geothermal industry.

The reservoir supplying WME-E1 is a shallow and highly productive 230 ℉ high -temperature system, which makes it attractive in terms of production and injection drilling costs.

Geothermometry results indicate higher temperature potential. Deeper drilling could reveal a hotter, deeper reservoir and will help characterize the complex geological controls on the Surprise Valley geothermal system. A hotter resource will increase opportunities for Modoc County to apply the resource for economic development, build energy self-sufficiency and resiliency, and assist California in meeting its clean energy goals. Further, the study helps validate geothermal research methods and previous findings, build confidence and understanding about the geothermal potential, and, in turn, streamlines future exploration with reduced risk.