Coupled One-Dimensional Subsidence Modelling Using Elastic-Plastic Rheology

Abstract

Subsidence as a result of extraction of geothermal fluids for energy production is a significant problem at many sites around the world. At the Wairakei geothermal field in New Zealand, subsidence has occurred since the onset of production in the 1950s. Subsidence is non-uniform and reaches as much as 15m in a small area known as the Wairakei subsidence bowl. The subsidence there is attributed to a reduction of pore pressure in the Huka Falls Formation (HFF), which is composed of pumice breccia and mudstone. The study described here uses a one-dimensional model to investigate subsidence at Wairakei. It is based on coupling the TOUGH2 heat and mass flow simulator with the ABAQUS solid mechanics modelling package through the use of Python scripting. We have used recent field data not available for past subsidence modelling exercises. The results from a linear elastic model are compared with the previously published work of Allis & Zhan (2000).