Ohaaki West Bank Production Fluid Compositions

Abstract

During 2006 and 2007 Contact Energy undertook a successful well drilling programme to increase the resource capacity and power production from the Ohaaki Geothermal Field with eight new wells drilled on the West Bank. This enabled a doubling of nett generation from about 30 to 60 MWe. A conservative production management approach has been taken seeking to avoid deleterious calcite scaling and drawdown of cooler surficial fluids.

Of the eight new wells, two discharge fluid similar in terms of TQZ, ClQZ and SO4QZ, to the fluid initially produced (in 1995) and presently discharging from BR48; that is relatively cool at ~260oC and dilute. Three of the remaining six new wells discharge aquifer fluids at TQZ ~290oC which is hotter than any of the presently discharging wells, indeed hotter than wells at the commencement of production in 1988. The last three wells discharge fluid with reservoir TQZ temperatures of ~280oC which was similar to those observed at the commencement of production. That six of the new wells discharge reservoir fluids which have been minimally affected by both dilution as well as boiling as a consequence of previous production is a good outcome for the future generation from Ohaaki.