Proceedings of the 6th New Zealand Geothermal Workshop 1985. Analysis of subsurface compaction and subsidence at Wairakei geothermal field. New Zealand Geothermal Workshop [7-9 Nov. 1984, New Zealand].

Robertson, Ann.

[1984]

CIENA
171

0-86869-056-2

Using the simple theory of one dimensional consolidation, close agreement between calculated compaction and observed subsidence was found for Wairakei geothermal field. The crucial parameters in the analysis are the compressibilities and thicknesses of the various formations and one magnitude of the observed decline in pore pressure and the level of the water table. the compaction of the surficial pumice and the underlying Wairakei Breccia and Huka Falls formation accounts for most of the observed subsidence. The reservoir pressure has always been lower in the eastern part of Wairakei Field than in the western part. Production of steam from shallow wells and cold water intrusion at relatively shallow levels in the eastern borefield contributes substantially to the reduction in steam pressure, which induced compaction in the Huka falls formation. The decline in the level of the water table results from the pressure reduction and causes the compaction of the two layers above the Huka falls formation. Precise modelling of subsidence at Wairakei is difficult because of the lack of data regarding the nature and thickness of the compaction-prone deposits and the uncertainty about subsurface conditions in the area of maximum subsidence, which lies outside the main production zone. Since deformable lacustrine sediments are also found at Ohaaki geothermal field, attention is drawn to the problem of potential subsidence at Ohaaki.

Presenta diagrs., gráfs., maps. y tbls.

NUEVA ZELANDIA; ENERGIA GEOTERMICA; CAMPOS GEOTERMICOS; INGENIERIA DE RESERVORIO; INVESTIGACION; VAPOR; PRESION;