| Abstract |
In December 2010, the 15 MW Jersey Valley geothermal plant, operating an Ormat Energy Converter (OEC), was successfully brought online. The culmination of fast-paced exploration and development, initiated in late 2006, the Jersey Valley geothermal project illustrates the challenges inherent in the cultivation of greenfield geothermal projects, yet exemplifies the skills and determination necessary to mitigate risk and actualize the objective. An overview of the Jersey Valley hydrothermal system is presented along with an account of the geoscientific and engineering efforts utilized to characterize the resource from the early exploration to later development phase. Perched at the northern end of Dixie Valley, along the Pershing/Lander county line in north-central Nevada, the resource is situated within the Basin and Range physiographic province and characterized by narrow, north-northeast-trending tilted block-faulted mountains separated by similarly aligned, alluvial-filled basins. Jersey Valley itself is bounded by the Fish Creek Mountains to the east and the Tobin Range to the west. The contemporary hydrothermal system is associated with active hot-springs and an extensive zone of opal and opal cemented alluvium localized along an east-northeast-striking subsurface relay-ramp, which transfers strain across major right-stepping north northeast–striking, down-to-the west, normal fault segments. The hydrothermal reservoir is interpreted to be the result of tectonics associated with a complex accommodation and transfer zone within northern Dixie Valley. This zone marks the transition from down to the east normal faulting along the Stillwater rangefront fault to down to the west normal faulting along the Augusta Range, and Fish Creek Mountains. The currently exploited portion of the Jersey Valley geothermal reservoir consists of a localized high temperature (>330°F) high permeability production area surrounded by a large low to moderate permeability reservoir. High productivity was measured by short flow tests of wells in the productive area, but moderate to low permeability was indicated by short flow tests of wells outside the productive area and by long flow tests of the productive wells. High pressure drawdown was predicted by a simple analytical model and confirmed by a complete reservoir model. Production pumps were set deep to accommodate the drawdown and performed as predicted in long-term operation. Operation of Phase I continues but, as in all developed geothermal fields, does not conclude Ormat’s efforts to understand and characterize reservoir parameters and potential. |