3D Conceptual and Numerical Model of Geyser Valley, Wairakei Geothermal Field New Zealand
Author: Madison Mackenzie
Year: 2022
Supervisors: Dr. Juliet Ann Newson
Abstract:
Geyser Valley, currently known as Wairakei Valley, is a small valley located within the geothermal field of the Wairakei Powerplant in Wairakei, New Zealand. Geyser Valley was once a beautiful landscape filled with geothermal wonders such as geysers, mud pots, sinter terraces, and hot springs prior to geothermal production of the field in 1951. Post-production the fluid flow into the valley ceased and turned into an area of steaming ground, it was then hypothesized that the fluid flow into the valley is heavily influenced by production and the pressure within the geothermal reservoir. This is supported by geochemical analysis regarding the Cl− concentrations of the features within the valley. The fluid that once flowed to the surface in Geyser Valley is hypothesized to have traveled from the geothermal reservoir through a fault, subjected to boiling causing a small steam zone to form just below the surface, and then infiltrated by a secondary shallow source of cool Cl− rich waters before flowing out at the surface. To study this phenomenon two models were created and tested, a conceptual model and a numerical model. The first 3D geologic model was created using Leapfrog Geothermal, a Seequent modeling software, then a conceptual model of processes in the subsurface was created. The second, a numerical model utilizing the mass fractions of the two water sources and relative permeabilities between the liquid and vapor in the subsurface. The results of the models show the geology of Geyser Valley, a possible permeability structure, and how the geothermal and diluting fluids are mixing, supported by comparing the calculated Cl− concentrations and the real-life Cl− concentrations from Geyser Valley. This thesis does show that the hypothesis of boiling in the reservoir upflow into Geyser Valley can be modeled, and the degree of detail in the geologic and conceptual model are able to provide a basis for more detailed numerical modeling.