GEOTHERMAL PLAY FAIRWAY ANALYSIS OF THE SNAKE RIVER PLAIN, IDAHO

Play Fairway Analysis (PFA) is a methodology that integrates data at the regional scale to define favorable plays for exploration and specific prospects with lowest risk and highest chance of success. The Snake River Plain Geothermal PFA project is one of several funded by the Department of Energy’s Geothermal Technology Office to stimulate new approaches to geothermal exploration.

During Phase 1 we compiled existing data at a regional scale and created a methodology in GIS for analyzing the three components needed for a geothermal energy system: heat, permeability, and seal. Each of these was modeled by combining a range of evidence and uncertainty layers to create Common Risk Segment (CRS) maps. These CRS maps were then combined to create a Composite CRS (CCRS) map that allowed us to select a variety of potential focus sites for further study. We use standard Arc GIS functions to process the data (e.g., empirical Bayesian Kriging, kernel density functions) and employ Python scripts to systematize data handling across layers. The resulting tools are both reproducible and portable to other regions and settings.

During Phase 2 we selected two representative focus sites, the Western Snake River Plain (WSRP) near Mountain Home, Idaho, and Camas Prairie in central Idaho. The Mountain Home region represents a blind geothermal resource in an area of high heat flow and young volcanism; Camas Prairie is a structurally controlled basin with indicators of magmatic heat. Phase 2 had three primary goals: (1) to fill data gaps in critical areas in order to better define potential prospects, (2) to integrate these data into new thermal and structural models, and (3) to infer the location of potential resources and drilling targets that could be validated during Phase 3.

New data acquired during Phase 2 included mapping and structural analysis of faults and subsurface lineaments; seismic, magnetotelluric, gravity and magnetic surveys; trace element and isotope geochemistry springs and well water; whole rock analysis of volcanic rocks, and new Ar-Ar ages of young basalt vents. We also produced new thermal models. Integration of these data into new higher resolution CRS and CCRS maps have identified two prospects for potential verification during Phase 3, which begins Fall 2017 and will include drilling a new test well in Camas Prairie.