| Title | Preliminary Geothermal Resource Assessment of the St. Helens Seismic Zone Using the Results from the Geothermal Play-Fairway Analysis of Washington State Prospects |
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| Authors | Michael W. SWYER, Matthew E. UDDENBERG, Trenton T. CLADOUHOS, Alexander N. STEELY, Corina FORSON, Nicholas C. DAVATZES |
| Year | 2018 |
| Conference | Stanford Geothermal Workshop |
| Keywords | St. Helens Seismic Zone, play fairway analysis, geothermal exploration, seismic, geophysics, geomechanics, resource assessment |
| Abstract | The northern St. Helens Seismic Zone was one of the areas of interest during Phase 2 of the Washington State Play-Fairway analysis. The area is assessed for geothermal resource potential using the volumetric reserve estimation method developed by the US Geological Survey. Multiple hypotheses for reservoir volume are proposed and analyzed based on interpretation of data gathered during Phase 2 within a geothermal lease. The data utilized in the analysis includes new geologic mapping, ground-based gravity survey, magnetotelluric survey, and passive seismic survey. The hypotheses will be tested, and the resource model will be updated after temperature gradient holes are drilled in the area during Phase 3 at sites selected from Phase 2. The analysis also makes use of the prior geologic knowledge of the area, including the increased seismic and geodetic monitoring following the eruption of Mount St. Helens on May 18th, 1980, existing geologic mapping and models developed from seismic and geodetic data, and past geothermal prospecting efforts by the Washington Division of Geology and Earth Resources. The analysis uses reservoir temperature from geochemistry and a single temperature gradient hole for a low value, and a temperature required for steam flash as a high value. Subsurface temperatures, and heat flows are expected to be better constrained after Phase 3 drilling. The preliminary results suggest power generation potential ranging from 65 MWe to 1.5 GWe within the lease area. |