Experimental and numerical studies on fluid–granite interaction for chemical stimulation in Enhanced Geothermal Systems (EGS)

Porosity generation and permeability maintenance in low-porosity rock systems are crucial for Enhanced Geothermal Systems (EGS), as they enable efficient fluid flow and transport while enhancing heat exchange in low-permeability reservoirs. In EGS, reactive transport processes, triggered by chemical stimulation, drive dynamic changes in mineral composition and petrophysical properties. However, the parameters that control the efficiency of chemical stimulation of granitic rocks are incompletely understood and experimental studies are still scarce.

In this study, we investigate reactive transport processes by performing batch and flow-through experiments, analyzing the interactions of granites with acidic F-bearing aqueous fluids under simulated geothermal reservoir conditions. Our experiments aim to understand and quantify the reaction-induced porosity and permeability increase of low-porosity granite systems using fluid compositions relevant for the chemical stimulation of EGS.

We used X-ray powder diffraction (XRD) and scanning electron microscopy (SEM) to characterize and quantify mineralogical changes while assessing the microstructural evolution of granites exposed to reactive fluids.

Our first experiments have demonstrated that significant porosity is created through chemical stimulation of low-permeability granite, driven by preferential dissolution of feldspar and mica in the host rock and the precipitation of amorphous silica and denser F-bearing phases that pseudomorphically replace the original mineral assemblages.

The chemical stimulation in the laboratory can be reproduced by reactive transport modeling. Our one-dimensional (1D) numerical model with different experimental parameters aim to recreate results from experiments, providing insights into the evolution of the system’s composition and petrophysical properties and predicting the potential for EGS reservoir development.