CHALLENGES AND ADVANCES OF GEOCHEMICAL MODELING IN CARBON AND HYDROGEN STORAGE IN GEOLOGIC SYSTEMS

Geochemical modeling is an indispensable tool for carbon dioxide and hydrogen storage in geologic systems because a series of water-CO2-H2-mineral-microbial reactions occur upon injection. However, creditable predictions of the fate of stored gases require us to understand both the fundamental science of geochemical reactions and databases that support the modeling applications. On the basic science front, recent innovative research on applying non-traditional stable isotope tracers has broken new ground in near-equilibrium reaction kinetics. Isotope-doping experiments illuminate that irreversible reactions for feldspar weathering reactions mean unidirectional dissolution and how we should model these reactions accordingly [1]. Second, several geochemical modeling codes and databases became available, which includes SUPCRTBL [2], Online PHREEQC, CO2 Solubility Calculator [3], and H2S Solubility Calculator [4] as well as thermodynamic and kinetic rate constant databases [5]. Notably, the Online PHREEQC program together with our customized databases now allows speciation and solubility and reaction path modeling to temperature up to 1000 oC and pressure up to 5000 bars. This presentation will show these recent studies. Challenges remain as information is scarce about near-equilibrium kinetics and reactions are coupled in multi-mineral systems.

[1] Zhu, C., J.D. Rimstidt, Y.L. Zhang, J.T. Kang, J. Schott, and H.L. Yuan. 2020. Decoupling feldspar dissolution and precipitation rates at near-equilibrium with Si isotope tracers: Implications for modeling silicate weathering. Geochimica et Cosmochimica Acta 271: 132-153.

[2] Zimmer, K., Y.L. Zhang, P. Lu, Y.Y. Chen, G.R. Zhang, M. Dalkilic, and C. Zhu. 2016. SUPCRTBL: A revised and extended thermodynamic dataset and software package of SUPCRT92. Computers & Geosciences 90: 97-111.

[3] Duan, Z.H., R. Sun, C. Zhu, and I.M. Chou. 2006. An improved model for the calculation of CO2 solubility in aqueous solutions containing Na+, K+, Ca2+, Mg2+, Cl-, and SO42. Marine Chemistry 98 no. 2-4: 131-139.

[4] Ji, X.Y., and C. Zhu. 2012. A SAFT equation of state for the quaternary H2S-CO2-H2O-NaCl system. Geochimica Et Cosmochimica Acta 91: 40-59.

[5] Lu, P., G.R. Zhang, J. Apps, and C. Zhu. 2022. Comparison of thermodynamic data files for PHREEQC. Earth-Science Reviews 225: 103888.