--> --> Play fairway analysis for structurally-controlled geothermal systems in the Eastern Great Basin extensional regime, Utah, USA

AAPG Pacific Section and Rocky Mountain Section Joint Meeting

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Play fairway analysis for structurally-controlled geothermal systems in the Eastern Great Basin extensional regime, Utah, USA

Abstract

We have carried out a play fairway analysis (PFA) for geothermal prospectivity in the Eastern Great Basin extensional tectonic regime of western Utah integrating several favorability indicators, with a key role by magnetotellurics (MT). Active Basin and Range style extension with volcanism having a N-S strike is superimposed upon pre-existing E-W belts of plutonic rocks and large-scale structural lineaments, inducing localized volumes of dilatency. Cumulative heat flow along the N-S strike of the state totals approximately 5 GW above background stable interior and there are three electricity producing power plants currently. 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 since the 1970s. Criteria selected for establishing heat potential include direct heat flow measurements, MT low resistivity, seismicity swarms, fluid geochemistry, and proximity to recent volcanism. In particular, high-temperature systems commonly appear to connect via steep, low-resistivity crustal fault systems to deeper magmatic sources. Permeability is established by fault density, by identification of critically stress areas, and by MT low resistivity. Heat source and permeability potential are expressed in terms of their individual common risk segment maps. To integrate disparate data types, the technique of probability kriging is adopted to derive map layers showing the probability (0 - 1) that a quantity exceeds a favorable threshold. These normalized data then are weighted in a multi-criteria decision making analysis to estimate overall prospectivity. East-west lineaments intersecting north-south rift structures appear to control location of several geothermal upwellings.