Comparison of Coupled One-Dimensional Subsidence Models

Abstract

Subsidence as a result of the extraction of geothermal fluids for energy production is a significant problem at many sites around the world. At Wairakei geothermal field in New Zealand, subsidence has occurred since the onset of production in 1958. Subsidence is non-uniform and reaches as much as 15m in a small area known as the Wairakei subsidence bowl. The high level of subsidence is caused by a reduction of pore pressure in soft patches in the Huka Falls Formation (HFF), which is composed of pumice breccia and mudstone. In this study, one-dimensional models are used to investigate subsidence at the Wairakei Bowl. Two different approaches are used for handling compaction: the first couples a TOUGH2 simulation of heat and mass transfer with a simple manual calculation of compaction, while the second uses FEHM to calculate both the heat and mass transfer and the rock deformation. The results obtained using each approach are compared with field measurements from Wairakei and with previously published work (Allis & Zhan, 2000).