| Title | The effect of CO2 reinjection on silica scaling in geothermal reservoirs |
|---|---|
| Authors | D.J. Byrne, J.W. Patterson, P.M. Rendel, B.W. Mountain |
| Year | 2023 |
| Conference | New Zealand Geothermal Workshop |
| Keywords | NCG reinjection, emissions, CO2, reactive transport, geochemistry, scaling |
| Abstract | The capture and reinjection of the noncondensable gases (NCG) that are associated with geothermal brine production is a key technology to ensure that geothermal energy remains a sustainable part of Aotearoa’s transition to a low carbon economy. Whilst several pilot schemes are underway to trial the viability of NCG reinjection, its potential effects on reservoir geochemistry are not well understood. Here, we present a combined experimental and modelling approach to investigate the effect of the incorporation of CO2 (the primary component of the NCG fraction in NZ geothermal brines) into reinjected brines. Four experimental reinjection simulations were performed in high-PT flow-through reactors under geochemical conditions relevant to New Zealand geothermal reservoirs, with varying levels of added CO2. The empirical observations collected as part of these experiments were used to constrain the rate parameters of a reactive transport model built using PFLOTRAN that can accurately reproduce the geochemical behaviour of the experiments. This numerical model can then be used to extend our investigation to the relevant spatial and temporal scales required to understand the long-term reservoir response to NCG reinjection. We show that for acid-dosed brines, addition of CO2 can significantly reduce the rate of silica scaling in reservoir. This has significant implications for reducing the injectivity decline of reinjection wells, which may help realise previously underappreciated cost savings achieved by NCG reinjection technologies. We demonstrate a framework whereby this combined experimental modelling approach can be used to quantify the effect on silica scaling for any brine-reservoir rock combination, with the aim of helping to de-risk and accelerate the deployment of NCG reinjection technologies across the NZ geothermal sector. |