ADAPTING SURFACE FACILITIES TO CHANGES IN ROTOKAWA RESERVOIR IN THE FIRST 5 YEARS OF NGA AWA PURUA

Abstract

The Rotokawa geothermal field has performed well during the five years since the commissioning of Nga Awa Purua Power Station, which brought about a five-fold increase in electrical output from the field. A process of careful monitoring supported by predictive modelling and evaluation of enhancement opportunities has been required to ensure this success. Pressure drawdown and chemistry trends in the reservoir have meant that changes to the production/injection strategy have been directed at improving the response of the field. The production to both power plants has experienced declining enthalpy pointing to a need for adaptive changes to maintain efficient operation over the plant lifetime. Nga Awa Purua has a centralised triple-flash steam separation arrangement and as a result its maximum output is sensitive to off-design fluid delivery conditions. The longer-standing second power plant, Rotokawa, also has a high-pressure fuelling requirement using an interconnected gathering system with aging wells. This paper summarises the experience and the optimisation, control and flexibility measures incorporated into plant and steam field operation.