A Preliminary Conceptual Model for the Blue Mountain Geothermal System, Humboldt County, Nevada

Abstract

Geothermal exploration at Blue Mountain in northern Nevada has proven the presence of a viable resource, leading to the development of a 49.5 MWe-gross binary power plant. Surface mapping has documented extensive faulting, fossil hot springs, and significant hydrothermal alteration along the western Blue Mountain range front. Drilling and testing of thermal gradient wells, slim holes and full-size wells (12.25” diameter) for production and injection provide direct observations of the lithologic, thermal, geochemical, and permeable character of the reservoir. Subsurface geophysical investigations are providing less direct observations of the system that are unavailable from drilling data. The resource is classified as a hot liquid-saturated convective system circulating neutral-pH, dilute alkali-Cl waters, with low to moderate contents of non-condensible gases. The reservoir is hosted within a fault and fracture network and fluids are circulated along a predominant NE-trending range front fault zone. The resource is an artesian reservoir at or below an elevation of ~1100 feet, which is calculated to be equilibrating to ~250°C at depth. Fluids produced for power generation are oversaturated with respect to silica causing a potential for scaling, however, this can be mitigated effectively by chemical inhibition. The risk of calcite deposition occurs only through adiabatic cooling and will not be problematic in the operation of the binary power plant.