| Title | Finding Sufficient Permeability for Outfield Injection and Recent Drilling at Kawerau, New Zealand |
|---|---|
| Authors | John CLARK, Sarah MILICICH, Steven SEWELL, Mohsen ASKARI and Charis WONG |
| Year | 2015 |
| Conference | World Geothermal Congress |
| Keywords | Kawerau, injection, alteration, fluid inclusions, outfield injection wells |
| Abstract | Kawerau is a multi-tapper field with Mighty River Power (MRP) and Ngati Tuwharetoa Geothermal Assets (NTGA) both having to ensure they have sufficient injection to maintain operations at full capacity, as well as providing a balance between maintaining pressure support to the field and preventing thermal breakthrough to the production areas. The Kawerau injection strategy considers a holistic reservoir view that includes numerous factors in determining the suitable locations for sustainable fluid injection. These include the proximity to the reservoir, results of geophysical resistivity surveys, the area of land available, the risk associated with the level of data known, the need to spread injection out, the position on or off suspected deep fluid pathways, and land access. Prior to 2013, all of the deep injection at Kawerau was situated on the geophysical fringe on the northwest of the field along the direction of the regional structural trend. In order to further spread injection loads and to move injection off-strike of the regional structural trend three new deep injection wells were drilled in 2013 to the north of the field outside of the resistivity boundary zone (Allis, 1997) based on Schlumberger resistivity surveys. Two were drilled by NTGA and the third by MRP. These wells presented significant step-outs and are situated about 1.5km from the known production areas. The injection wells encountered very good to moderate permeability with maximum temperatures of ~200¢ªC. Hydrothermal alteration corresponds well with more recent MT results allowing the identification of potential permeable areas outside of the previously defined field boundaries. Alteration mineralogy and fluid inclusion microthermometry from the three wells shows that in the north of the field geothermal activity was much hotter than present and that the area has undergone significant cooling. The injection wells are utilising deep permeability that had hosted past, high temperature geothermal activity. |