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Title: |
Reinjection into Liquid-Dominated Two-Phase Geothermal Systems |
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Authors: |
Eylem Kaya, Michael J. O’Sullivan and Kerin Brockbank |
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Key Words: |
Reinjection, Wairakei-Tauhara, modeling |
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Geo Location: |
Wairakei, New Zealand; Tauhara, New Zealand; Taupo Volcanic Zone |
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Conference: |
Stanford Geothermal Workshop |
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Year: |
2011 |
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Session: |
Injection |
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Language: |
English |
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Paper Number: |
Kaya |
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File Size: |
280KB |
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View File: |
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A 3D numerical model of the Wairakei-Tauhara field is used to investigate the effect of reinjection on liquid-dominated two-phase geothermal systems. Wairakei-Tauhara is an interesting case study as it has been operated with no reinjection for most of its lifetime. Several scenarios are run with the model to test what would have happened if different reinjection strategies had been followed. The impacts of different rates of outfield and infield reinjection on production enthalpy, reservoir pressure and temperature, recharge conditions and surface features are investigated.
Our modelling results show that infield reinjection has two negative effects on energy production. The first and major effect is that infield reinjection suppresses boiling and therefore decreases the average production enthalpy. Secondly as reservoir pressures are maintained by infield reinjection, deep hot water recharge to the system is suppressed and replaced by the much colder injected fluid. These two effects are small for low levels of infield reinjection (up to 25% of the separated water) and therefore this appears to be a good infield reinjection strategy.
Reinjection has an important effect on surface features. With no reinjection the large pressure drop caused by production results in a decrease over time in the flow of chloride water from the deep aquifers to the surface features. Also with no reinjection shallow boiling zones may develop in some areas, and cause the ground surface above to become steam heated. Reinjection supports the flow of chloride water to the surface features, but at a lower temperature than in the natural state. However if the reinjection zone is close to the steam-heated surface features they may significantly decline or totally disappear.
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