Two dimensional subsidence modelling at Wairakei-Tauhara, New Zealand

Abstract

Subsidence at Wairakei-Tauhara due to almost 50 years of geothermal fluid extraction was modelled by two dimensional finite-element analysis. The software accommodates variable rock properties, including non-linear stress-strain behaviour, and pre-consolidation history. A good match to historical subsidence in time and space was achieved with a single set of rock properties for each geological unit, apart from two local zones with different permeability. Compared to previous 1-D subsidence modelling, this study shows a greater sensitivity to changes in reservoir pressure andstrong control over the location of subsidence by the morphology of the lowest unit in the Huka Falls Formation. It is predicted that subsidence may lead to subsurface shear failure, which will enhance vertical permeability, and therefore cause an acceleration of subsidence rates.