| Title | Geothermal Greenhouse Gas Emissions Reduction at Mercury Energy: Progress to Date and Challenges Ahead |
|---|---|
| Authors | John Mering, Ivo Lemmens, Jeff Yee, Sam Houwers, Emily Collis, Farrell Siega |
| Year | 2026 |
| Conference | World Geothermal Congress |
| Keywords | |
| Abstract | Mercury Energy Ltd. generates renewable electricity in New Zealand from wind, hydroelectric, and geothermal sources. Since 2021, the company has been pursuing an ambitious geothermal greenhouse gas emissions reduction strategy across its fleet of binary and flash plants. Mercury began noncondensable gas (NCG) reinjection at the Nga Tamariki binary station in October 2021. Currently, the gases from two out of four binary OEC units are being reinjected into two wells, at a rate of ~1-1.5 t/hr CO2-equivalent, delivering a 40% reduction in annual greenhouse gas emissions to the atmosphere. Planning is underway to reinject 80% of produced NCGs at Nga Tamariki by collecting and reinjecting the gas from the remaining two binary units. NCG reinjection at Mercury’s two flash plants presents additional challenges not encountered at binary sites, with respect to air contamination of the gas stream, low outlet pressures, and the overall amount of NCG to be reinjected (70-100 kt/yr). Addressing these challenges will involve a combination of technology adaptation and process optimisation. The objective of this presentation is to provide a high-level summary of Mercury’s geothermal emissions reduction program and progress to date. Key technical hurdles described include understanding gas solubility constraints in pipelines and wells, gas cleanup and compression requirements, scaling and corrosion monitoring and mitigation, and understanding the fate of reinjected NCGs in geothermal reservoirs. To meet these challenges, Mercury relies on interdisciplinary teams of engineers and geoscientists, and benefits from collaboration across the wider industry. |