| Title | Investigations of reservoir response to net negative CO₂ reinjection using full scale geothermal reservoir models |
|---|---|
| Authors | A. Swanepoel, M. Raihannur, A. Karan, M. Gravatt, R. Tonkin, J. OSullivan, J. Riffault, M. OSullivan |
| Year | 2024 |
| Conference | New Zealand Geothermal Workshop |
| Keywords | Geothermal, Reservoir modelling, Numerical modelling, CO₂ reinjection, Net zero, Net negative, Waiwera |
| Abstract | Geothermal power production is a renewable form of baseload electricity generation. However, it is not an emissionsfree process due to non-condensable gases, such as CO₂ found naturally underground that are mixed into the working fluid. With the global push toward more sustainable operation of infrastructure, good management of the CO₂ emissions in geothermal fields has financial, environmental and cultural benefits. One strategy is to inject 100% of the CO₂ produced by the system in what is known as a net zero reinjection scheme. Furthermore, additional CO₂ can be captured from other processes, such as the burning of biomass fuels in hybrid biomass geothermal power generation plants and added to the existing reinjection streams. This is known as a net negative injection scheme. However, successful sequestration of CO₂ using these methods requires knowledge of how the reinjection strategies affect the system, particularly relative to its natural state. Directly monitoring all CO₂ emissions across the surface of the geothermal system in sufficient detail is impractical. Estimation of these emissions can be done using numerical modelling, where short-term CO₂ accumulation under the clay cap is used as a proxy for CO₂ emissions in the long term. This project used a synthetic model to perform numerical simulation of a no CO₂ reinjection production scenario, a 100% CO₂ reinjection scenario and a 110% CO₂ reinjection scenario using Waiwera, an open-source geothermal flow simulator. In the case with no CO₂ reinjection we observe a steady decline in production CO₂. The two cases where we reinject CO₂ (100% and 110%), we show production CO₂ is consistent with the base case for the first 3.5 years, then we observe a steady increase over the duration of the simulation. In the base case, CO₂ leaves the model either through production or the surface. When injection of CO₂ occurs, the CO₂ is replenished in the production zone of the reservoir from reinjection and the up flow resulting in elevated CO₂ production and more CO₂ going through the alteration in time. |