Reservoir Pressure Drawdown and the Alum Lakes, Wairakei

Abstract

The local groundwater system and surface geothermal features such as geysers, boiling pools, mud pools, and steaming ground at Wairakei, New Zealand, have been strongly affected by 50 years of fluid extraction from the underlying Wairakei geothermal reservoir. For this study we have used geothermal reservoir and surface water data to calibrate a two-dimensional (2-D) numerical model, using the TOUGH2 geothermal simulator (Pruess, 1991), which links reservoir drawdown to changes in geothermal outflow from the Alum Lakes area of the Wairakei system. The 2-D model is based on an existing three-dimensional (3-D) computer model of Wairakei system, but uses a finer grid in the vicinity of the Alum Lakes. The model shows that pressure decline in the Wairakei reservoir has resulted in a cessation of the geothermal upflow to the overlying Alum Lakes, and the Alum Lakes feeder conduit now hosts a down flow of groundwater.