A Play Fairway Analysis for Structurally Controlled Geothermal Systems in the Eastern Great Basin Extensional Regime, Utah

Abstract

A research team with membership from the University of Utah/Energy & Geoscience Institute, and the University of Utah/Dept. of Geology & Geophysics, have carried out a play fairway analysis (PFA) for geothermal resources in the Eastern Great Basin extensional tectonic regime of western Utah. Here, active Basin and Range (B&R) extension with volcanism having a N-S strike is superimposed upon pre-existing E-W belts of plutonic rocks and large-scale structural lineaments. Cumulative heat flow along the N-S strike of the state totals approximately 5 GW above background stable interior. Three electricity producing power plants currently exist with potential for greatly increasing this number. Our PFA adds to understanding of the potential sources of heat and permeability in the region, which are the two principal criteria for establishing a geothermal resource. An advantage of this PFA region is the relative abundance of existing data, related to a substantial history of geothermal exploration in the region. Criteria selected for establishing heat potential include direct heat flow measurements in boreholes, magnetotelluric (MT) low resistivity anomalies, fluid geochemistry, and proximity to recent volcanic eruptions. Permeability is established by fault density, by identification of critically stress areas, and MT low resistivity anomalies. Heat source and permeability potential are expressed in terms of their individual common risk segment maps, with a color scheme using green for most favorable (low risk) and red for least favorable (high risk). Due to data quantity, statistical approaches to defining risk, together with good conceptual models of the area, lead to several followup recommendations. Two east-west conductive lineaments, one coincident with the Cove Fort transverse zone and one nearby to the north which we name the Twin Peaks-Meadow zone, appear to be controlling structures for several local fluid and heat upwellings such as Cove Fort, Twin Peaks, and several previously unnamed prospects. Priorities for followup include southward swath extension and detailed fill-in MT coverage, passive helium transect surveying, and detailed structural investigation.