Deep Exploration of the Ohaaki Geothermal Field

Abstract

The Ohaaki geothermal field is typical of those in the Taupo Volcanic Zone in New Zealand, having high penneability and relatively high temperatures at shallow depths. The wells drilled at Ohaaki from the mid 1960's to the mid 1980's, produced 240-280°C geothermal fluid from volcanic derived formations between 400 and 1000 m depth. Production-induced pressure draw down since the Ohaaki Power Station was commissioned in 1988 has resulted in an influx of cool water into the shallowest production zones, and decline in steam production. In 1995 three exploration wells were drilled to investigate the production potential of the greywacke sediments that were known to be present below the volcanic fonnations. Permeable zones were not found within the hot greywacke. Target zones for deeper production from 280-300°C fluid were identified towards the bottom of the volcanic sequence and BRl5 and BR49 are presently producing about 12 MWe from these zones.