Reinjection as a solution to greenhouse gas emissions from high emitting geothermal power plants in New Zealand

The purpose of this paper is to discuss emissions from geothermal power plants in New Zealand. Geothermal energy has been considered as a clean and sustainable source of energy. However, the geothermal fluid also contains the greenhouse gases which are emitted to the atmosphere after the electricity generation process. Releasing the gases to the environment after the electricity generation process is neither environmentally suitable and may not be economically feasible if the price of carbon increases. These emissions have become an issue of major concern with the draft advice of the climate change commission recommending that high emitting power stations be closed by 2030. Reinjection of the fluid and the gases back to the reservoir or using CO2 for industrial and agriculture purpose seems to be a viable solution towards achieving a zero-carbon emission target. Reinjection of separated brine is routinely carried out and plays an important role in the geothermal system as it provides pressure support which acts as a barrier to cold water recharge to the reservoir and reduces environmental impacts by deposing water back to the reservoir. Though reinjection provides a feasible solution to the water disposal problem, it can also harm to the reservoir by creating problem such as thermal breakthrough. Therefore, we need well planned and modelled strategies for reinjection systems, that are site-specific as the geologic setting differs from site to site. This paper will provide a qualitative understanding of the various reinjection strategies in New Zealand and the response of the geothermal system to those strategies. If the CO2 gas from a geothermal power plant is reinjected into the reservoir there may be impacts on surface features which may impact economic and cultural factors. This work will outline a study that will be undertaken to optimize the strategy for reinjecting CO2 gas into a geothermal reservoir. The optimization will consider the impacts on power generation, surface features and other factors. Index Terms—Greenhouse gas emissions, geothermal, reservoir, gases, reinjection, emissions.