Resource management of the Brady Geothermal Field (Nevada)

Brady Power Partners (BPP) has operated a 20 MWe dual-flash electrical power
plant at the Brady Geothermal Field in Nevada (Brady’s) since 1992. BPP’s operations
obtain geothermal water from pumped production wells drilled into the Brady’s
fault zone. From the beginning of operation, cooling of production by breakthrough
from injectors, drilled into the fault zone about 1600 meters further north, has been a
problem. To aid in resource management, BPP initiated a comprehensive technical
appraisal of the Brady’s geothermal resource in the late 1990’s. The first phase was a
detailed geologic assessment that included a review of pertinent regional geology, a
three-dimensional definition of the Brady’s thermal anomaly, the identification of
important stratigraphic units and their characteristics, and a detailed interpretation
of subsurface geologic structure. The result was a comprehensive conceptual geologic
model of the Brady’s resource. In the second phase, this conceptual geologic model
was used as the basis in developing a fully calibrated numerical model of the resource
using TETRAD reservoir simulation software. The model was used to make quantitative
forecasts of reservoir performance under various scenarios. The scenarios
explored the tradeoff between remote injection (to arrest the field’s cooling) versus
in-field injection (to support the field’s pressure and productivity). These scenarios
were compared and the final operating plan consisted of diverting a specific amount
of injection to a remote area and installing a 5.0 Mw binary bottoming cycle plant to
operate on the effluent of the existing flash plant. With two years of binary operation,
the numerical model continues to closely match the measured data and the installation
of the binary has been successful.