A Simple Basin and Range Fault Model for the Beowawe Geothermal System, Nevada

Abstract

Data from wells as deep as 9,500 feet indicated that the Beowawe geothermal system can be described simply as an inclined thermal plume within the Malpais fault zone (MFZ). Though curved in plan view, this Bain and Range structure dips at a consistent 65-70° and does not flatten with depth. Productive MFZ intercepts in wellbores are typically interpreted at zones of abundant fluid loss or bit drops during drilling and stabilized temperature maxima. Deep 420°F waters within the MFZ rise obliquely from the southwest toward discharge in the Geysers area, where there is a vigorous along strike flow in the fault at shallow depths. Permeability variations with the MFZ are shown by variation in permeability thickness products measured in well tests Regions of lower permeability in the MFZ seem to occur on margins of the high temperature plume, suggesting self sealing and isolation of the plume from cooler portions of the fault. Permeable range front faults, parallel with but apparently hydrologically unconnected to the MFZ may be suitable injection site. The producing area should ultimately expand down dip of the Ginn and 85-18 wells, southwest of Ginn long the Malpais fault trend.