Conceptual Model Update and Power Capacity Estimate Hot Springs Bay Valley, Akutan, AK USA

Abstract

The initial conceptual model for the Hot Springs Bay Valley geothermal resource on Akutan Island, AK, has been revised in light of new data and interpretations. The 2012 conceptual model (Kolker et al., 2012) was based on exploration efforts beginning in 2008 and included data sets from an MT survey, fluid, gas and soil geochemistry, and data collected from two thermal gradient wells. The revised conceptual model incorporates additional geophysical data, targeted geological mapping, structural analysis, and the results from drilling and flow testing a third small-diameter well. The area of greatest geothermal potential is in the conceptualized upflow area, northwest head of the HSBV, where fluid and gas geochemistry data from fumaroles indicate a ~525°F (~275°C) reservoir. An outflow reservoir is also present, with cooler estimated reservoir temperatures (~356oF (~180oC) and reduced permeability estimates than the upflow area. The revised conceptual model is largely consistent with the original, providing sufficient confidence to estimate power capacity. The extent of surface alteration in the valleys east and south of the fumaroles suggest a range of possible reservoir sizes, allowing pessimistic, preferred, and optimistic power capacity estimates for both the upflow and outflow parts of the resource.