Forty Years of Production from the Steamboat Geothermal Field: Numerical Model Update

Abstract

The Steamboat geothermal field is a Great Basin geothermal system in Reno, Nevada, generating 79 MW net electricity using five zero-greenhouse gas emissions powerplants with full mass reinjection as of 2020. It has been in operation since 1987 and with consolidation of ownership under Ormat since 2004. A numerical reservoir model was developed, calibrated to natural state temperature and pressure conditions, measured production temperatures from 28 wells, the reservoir pressure history, and reservoir tracer tests conducted throughout the operational history. The numerical model honors the updated geologic and conceptual model for Steamboat, which is characterized by high-angle NE striking faults. These faults control the location of 220-240°C upflow beneath Steamboat Hills and contribute to the 3+ km-long NE-directed outflow to Lower Steamboat. In addition, there is evidence of distributed permeability in the host rock, particularly in Lower Steamboat where unloading features in the granodiorite may be responsible for low-angle faulting and high stratigraphic permeability. Production wells at Steamboat are located in both the upflow and lower temperature outflow of the system. Production temperature decline varies across different parts of the reservoir and is driven by factors such as permeability, and proximity to upflow and reinjection. The highly permeable faults and distributed permeability at Steamboat support high flowrates with low pressure interference and minimal long-term pressure decline. The large scale, long history and unique structural geometry of Steamboat geothermal reservoir is captured in this study as Ormat continues to optimize its development and operational strategy.