| Title | Insights from reactive transport models of basalt and water experiments |
|---|---|
| Authors | D.E. Altar, E. Kaya, S.J. Zarrouk |
| Year | 2022 |
| Conference | New Zealand Geothermal Workshop |
| Keywords | TOUGHREACT, reactive transport, numerical model, supercritical, basalt |
| Abstract | TOUGHREACT™ was used to create reactive transport models to match the results of detailed laboratory simulations of the interactions between tholeiitic basalt and distilled de-oxygenated water. The fluid-rock interaction experiments were carried out under two sets of conditions, one under subcritical conditions (350 °C and 490 bar) and the second under supercritical conditions (400 °C and 500 bar). The experimental environments are associated with seafloor spreading centres and mid-ocean ridges. Methodologies were developed for building the reactive transport models, focusing primarily on the reaction thermodynamics and kinetics parameters at high temperature and pressure conditions. Initial geochemical assumptions made for the models were also validated and updated during model calibration. Based on the model, precipitation rates deviated significantly from the combination of the estimated kinetic parameters and mineral surface area estimates, while there is an agreement in terms of dissolution rates. In concurrence with experimental results, mineral solid solutions dissolved stoichiometrically in the model except for bytownite, whose albite component was preferentially dissolved, resulting in its alteration to anorthite. The volumes of basalt glass in the samples were also higher than experimental estimates based on the models. Sulfide inclusions in the glass were added to the model assumptions to explain the observed sulfate and sulfide concentrations while the glass dissolved. The potassium concentration trends in the effluents also necessitated the inclusion of K-feldspar in the model system. |