PLAY FAIRWAY ANALYSIS IN GEOTHERMAL EXPLORATION: CASE STUDY IN SNAKE RIVER PLAIN VOLCANIC PROVINCE

The Snake River Plain (SRP) volcanic province overlies a thermal anomaly that extends deep into the mantle, representing one of the highest heat-flow provinces in North America. It has long been considered a target for geothermal development, but the lack of a conceptual model and systematic exploration has hindered this vision. Play Fairway Analysis (PFA) is a methodology adapted from the petroleum industry that integrates data at the regional or basin scale to define favorable plays for exploration in a systematic fashion. The success of PFA in geothermal exploration depends critically on defining a systematic methodology that is grounded in theory and adapted to the geologic and hydrologic framework of real geothermal systems.

This PFA focused on identifying three critical resource parameters for exploitable hydrothermal systems in the SRP: heat source (Heat), reservoir and recharge permeability (Permeability), and cap or seal (Seal). Data included in the compilation for Heat were heat flow, the distribution and ages of volcanic vents, groundwater temperatures, thermal springs and wells, helium isotope ratios, and reservoir temperature estimates from geochemistry. Permeability was derived from stress orientations and magnitudes, post-Miocene faults, and subsurface structural lineaments based on magnetic and gravity data. Data for Seal included the distribution of impermeable lake sediments and clay-seal associated with hydrothermal alteration below the regional aquifer. These data were integrated into a GIS platform and weighted and compiled to create a Composite Common Risk Segment (CCRS) map for all of southern Idaho that reflects the risk associated with geothermal resource exploration and identify favorable resource tracks.

Our findings identify significant prospective undiscovered geothermal resources in the western SRP associated with buried lineaments capped by lacustrine sediment, at lineament intersections in the central SRP, and along the margins of the eastern SRP. These blind resources are associated with temperatures sufficient to support electricity production, and may be exploitable with existing drilling technology.