Optimising reinjection capacities for Nga Tamariki power plant

Abstract

The Nga Tamariki (NTM) geothermal power plant relies on a northern and southern reinjection pipeline system to return geothermal fluids to the reservoir. Commissioning of the Nga Tamariki OEC5 unit will see the station’s reinjection demand increase from 2,300 t/h to 3,150 t/h. Reinjection capacity through the southern reinjection system will be constrained by significant pressure drop along the common DN450 pipeline. This paper presents a case study using a steady-state hydraulic model developed in AFT Impulse to evaluate the reinjection system from the station’s reinjection pumps through to the reinjection wells. The model incorporates as-built piping layouts and recent well injectivity data. Then it was calibrated using recent operating data from October 2024 pump trials to accurately reflect the pressure-flow profile. Various system modifications and scenarios were evaluated to meet the increased injection capacity, including:
• Reinjection pumps online and offline (bypassed) operation.
• Minor system modifications (New flow meters orifice plates and removing northern reinjection pipeline NCG static mixer).
• Major system modifications (New pipelines and repurposing redundant pipelines).
• Additional injection well cases (New wells and repurposing redundant wells)
The output of the hydraulic modelling was used to update the NTM Integrated Model (Reservoir, Steamfield and Station), enabling each case to be evaluated and ranked according to a 25-year project NPV. The overall analysis identifies optimal strategies and timing to enhance the reinjection capacity, ensuring reliable reinjection capacity at 3,150 t/h.