Current and future geothermal research in New Zealand

Research programs by Crown Research Institutes (Geological and Nuclear Sciences Ltd. and Industrial Research Ltd.), university departments (Auckland, Massey and Victoria), power companies and private consultancies aim to obtain a better understanding of currently producing geothermal fields in New Zealand, and of deep geothermal systems which might have potential for future resource development. Research is also being directed at industrial and environmental issues related to exploitation, water-rock alteration processes, changes in shallow geothermal systems with time, and mineralisation as it relates to epithermal ore formation. The chemical and physical environment of geothermal reservoirs in the Taupo Volcanic Zone (e.g. Thames, Kawerau, Ohaaki, Ngatamariki, Wairakei, Tongariro, Tauhara and Tokaanu-Waihi) is being quantified with the aim of developing a suite of magma to ambient production scenarios using numerical, reactive transport models. A variety of geological, geochemical and geophysical techniques including fluid inclusion geothermometry, stable isotope analysis, electromagnetic, micro-seismic and magnetotelluric analysis is providing high quality input data. Through experimentation and computer modelling, criteria for assessing the optimal depths for re-injection of production effluents are being developed, and related problems such as silica and calcite scaling, pipeline insulation and chemical corrosion investigated. Paths, flow mechanisms and flow rates of re-injection plumes are being modelled using electrical resistivity, micro-gravity and radioisotope tracer methods. Environmental effects related to testing and development, presently causing concern amongst local authorities and the public, are being quantitatively assessed, and recommendations made to mitigate them. The mechanical and petrological properties of rocks in shallow aquifers undergoing ground subsidence are being determined, and the extent and style of ground deformation investigated. Changes in surface heat flow and carbon dioxide flux are also being determined and the data obtained modelled to assess the use of shallow re-injection to resolve environmental problems. (author). 7 refs., 3 figs