| Title | GEOCHEMISTRY AND GEOTHERMAL PROSPECTIVITY OF THE HYDROCARBONPRODUCING TARANAKI SEDIMENTARY BASIN |
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| Authors | A.G. Reyes |
| Year | 2021 |
| Conference | New Zealand Geothermal Workshop |
| Keywords | Taranaki, petroleum, geothermal prospectivity, geochemistry |
| Abstract | In a previous nation-wide study of low-enthalpy geothermal systems in New Zealand, the Taranaki peninsula was deemed sixth of the six regions in New Zealand with the highest geothermal prospectivity, albeit the only one where the minimum estimated recoverable heat (0.54 PJ/a) and estimated temperature range (<100-200oC) are based on data from abandoned subaerial oil and gas wells. This submission examines fluid geothermometry in more detail as part of a study on the geochemical compositions of oil and gas well discharges and their effects on future geothermal exploitation. Bottomhole temperatures (BHT) of wells in Taranaki vary from <50oC to about 175oC. The highest subsurface temperatures (>150oC) based on solute chemistry occur at New Plymouth, Kapuni and Stratford, with moderate temperatures (100-150oC) at Onaero, Kaimiro, Ngatoro, McKee and Waihapa, and the lowest in the west at Te Kiri (<100oC). High temperatures at New Plymouth may be related to the shallowing of the upper mantle but high temperatures at Kapuni and Stratford may be due to rapid ascent of hot fluids via deep faults. Subsurface temperatures at Taranaki show that geothermal energy can be harnessed for power generation and direct heat use. Because of the likelihood of liquid condensation, the presence of gases >C6 would require a different distribution system for geothermal fluids for power or direct heat use if fluids from petroleum wells are directly harnessed for geothermal energy. However, the use of deep borehole heat exchangers at Taranaki may obviate the problem of hydrocarbon gas condensation and hydrocarbon solidification during geothermal production. |