| Title | GEOCHEMICAL RESPONSE OF THE ROTOKAWA RESERVOIR TO THE FIRST 5 YEARS OF NGA AWA PURUA PRODUCTION |
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| Authors | S.J. Addison, J.A. Winick, S.M. Sewell, E. Buscarlet, D. Hernandez, F.L. Siega |
| Year | 2015 |
| Conference | New Zealand Geothermal Workshop |
| Keywords | Rotokawa, geochemistry, Nga Awa Purua, dilution, silica, boiling, production |
| Abstract | Best practice field management requires identification of the key processes acting within the reservoir and understanding of the relationships between reservoir and process chemistry changes with the potential to impact resource and infrastructure sustainability. Following the initial development of the 34MWe Rotokawa Geothermal Power Station, the Rotokawa reservoir exhibited relatively stable production geochemistry characteristics. In 2010 the 138MWe Nga Awa Purua Geothermal Power Station (a joint-venture between Mighty River Power and Tauhara North No.2 Trust) was commissioned which increased steam production and brine injection in the Rotokawa reservoir. As anticipated, this generated a number of transient hydrogeologic changes in the reservoir which were monitored closely through regular Tracer Flow Testing (TFT), produced fluid geochemistry sampling, in addition to a variety of other reservoir testing activities. When integrated and evaluated within a geoscientific context, these data provide important insights into both transient and long-term reservoir changes which can occur in response to operational activities. This paper will discuss the geochemical response of the Rotokawa reservoir to Nga Awa Purua start-up and operation over the last 5 years. Production well geochemistry has identified three main geochemical responses within the reservoir: boiling, injection returns and dilution from marginal recharge. In addition, a transient increase in silica within the production fluids was identified that has stabilised over the last two years to levels which do not impact operational activities. |