Geothermal subsidence study at Wairakei–Tauhara, New Zealand

Geothermal, as a source of renewable energy (power and heating), has the potential to meet 3–5% of global demand by 2050. For some high-temperature reservoirs, a technical challenge that may constrain deployment is ground subsidence caused by reservoir pressure decline. At the Wairakei–Tauhara geothermal system in New Zealand, an integrated geotechnical-geoscientific investigation of the causes of local subsidence anomalies (up to 15 m, accumulated over 50 years) has successfully identified and modelled the factors, mechanisms and processes involved. Zones of hydrothermally altered porous sediments and clays, at up to 400 m depth, display inelastic deformation behaviour, yielding to a highly compressible state once subjected to a fluid pressure decline. Monitoring shows that pressure dissipates slowly through these low-permeability capping formations. Adaptive management involves continued monitoring of subsidence rates, and sampling, analysis and predictive modelling where necessary. Simulation modelling indicates that long-term mitigation can be achieved by sustaining pressures through targeted shallow injection.