Members of our GNG team recently co-authored a paper published in the Geothermics journal.

Altar, D.E., Kaya, E.,  Zarrouk, S.J., Passarella, M., Mountain, B.W. Numerical geochemical modelling of basalt-water interaction under subcritical conditions, Geothermics, 105, 102520 (2022). https://doi.org/10.1016/j.geothermics.2022.102520 

Reactive transport models are vital tools for understanding geothermal reservoir processes. They provide information on subsurface mineral alterations (dissolution and deposition), geothermal fluid chemistry evolution, dissolved gas content, and reservoir porosity and permeability distributions. In this paper, the authors undertook reactive transport modelling of a high pressure and temperature laboratory experiment that simulated the reaction between unaltered tholeiitic basalt and distilled water under subcritical conditions (350 °C and 490 bar). 

This modelling study was used to develop methodologies for building reactive transport models in TOUGHREACT™ with a particular focus on the parameters for reaction thermodynamics and kinetics at high temperature and pressure conditions. Equilibrium constants for mineral and aqueous reactions were estimated using SUPCRTBL (Zimmer et al., 2016). Mineral dissolution rates were primarily adopted from Palandri and Kharaka (2004), while precipitation rates were estimated following the work of Horiuti (1957).

The validation and update of geochemical assumptions are also integral to the methodology. Published reaction rates were verified against experimental results (using the effluent chemistry and mineralogy data) to supplement the currently available information for mineral reactions at the experiment temperature and pressure. Justifications for the modelling decisions made as well as uncertainties are presented. The methodology can be adapted for use with similar high temperature and pressure environments, including supercritical water conditions.

A satisfactory agreement was achieved between the experiment results and the numerical model. The calibrated reactive transport model sufficiently captured the mineral reaction kinetics and the interactions of the concurrent dissolution and precipitation processes in the experiment. The model is expected to provide realistic predictions of further interactions between distilled water and basalt at 350 °C and 490 bar if the experiment was run for a more extended period.

References

Horiuti, J., 1957. 35 A Theorem on the Relation between Rate Constants and Equilibrium Constant. In: Proceedings, International Congress on Catalysis. Philadelphia, Pennsylvania, pp. 339-342. https://doi.org/10.1016/S0360-0564(08)60183-2

Palandri, J.L., Kharaka, Y.K., 2004.A Compilation of Rate Parameters of Water-Mineral Interaction Kinetics for Application to Geochemical Modeling. U.S. Geological Survey, Menlo Park, California. Accessed from: https://pubs.usgs.gov/of/2004/1068/

Zimmer, K., Zhang, Y., Lu, P., Chen,Y., Zhang, G., Dalkilic, M., Zhu, C., 2016. SUPCRTBL: A revised and extended thermodynamic dataset and software package of SUPCRT92. Comput. Geosci. 90(Part A), 97-111. https://doi.org/10.1016/j.cageo.2016.02.013

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