Experiment-Based Modeling of Geochemical Interactions in CO2-based Geothermal Systems

Abstract

Carbon dioxide (CO2) has recently been considered as an alternative geothermal working fluid because of some favorable fluid dynamics and heat transfer properties compared to water. While the thermal and hydraulic aspects of CO2-based geothermal systems look promising, major uncertainties remain with regard to chemical interactions between fluids and rocks, particularly during the transition from resident water to supercritical CO2. We have performed reactive transport modeling to study fluid-rock interactions and its impact on porosity and permeability changes, based on batch experiments with rock and mineral samples and mixtures of water and CO2; these experiments are conducted at temperature and pressure conditions that are representative of typical geothermal systems. Different thermodynamic databases are tested, and the geochemical model is calibrated by adjusting the reactive surface area, as a representative rate controlling parameter, to fit the experimental data of mineral dissolution. The flow and geological conditions of a CO2 geological sequestration site at Cranfield, Mississippi are used for the modeling analyses. The objective of this research is to (1) investigate mineral dissolution and precipitation patterns, (2) evaluate associated porosity changes and effects on fluid and heat transfer, and (3) determine thermodynamic and kinetic reaction rate parameters that can be used to constrain coupled process models.