| Title | The Ohaaki Deep Reservoir |
|---|---|
| Authors | K M Brockbank, P F Bixley |
| Year | 2011 |
| Conference | New Zealand Geothermal Workshop |
| Keywords | Ohaaki, West Bank, deep production, high temperature, production decline |
| Abstract | The original exploration wells drilled on the West Bank section of the Ohaaki reservoir in the 1960s proved a very productive, high temperature resource at 450-1100m depth. Since production started a significant part of this resource has been invaded by cooler waters, reducing or stopping production in many wells. During 2005-2007 a deep makeup well program was undertaken to restore the lost production. Ten new wells were drilled; nine of these being deep wells located on the West Bank targeting permeability below the original production zones at 450-1100m. These deep wells proved an extension of the productive reservoir on the West Bank down to 2500m depth with temperatures up to 307°C. In retrospect, such an extension of the reservoir was implicit from the exploration wells drilled in this area during the 1960s, as many of these wells developed strong two-phase upflows while shut-in. After production from the new deep wells started in 2008, the deeper part of the reservoir developed a separate pressure regime about 40 bar lower than that in the overlying “intermediate” production aquifer. Maintaining production from the deep reservoir provides several challenges due to the large pressure drawdown and “cool” interzonal flows in some wells which have feedzones in the different aquifers. This paper outlines the development and evolution of the Ohaaki West Bank reservoir since production started in 1964. |