Coupled thermal-hydrological-mechanical-chemical (THMC) processes can significantly impact the long-term evolution of reservoir permeability, associated with geothermal energy extraction (

Formation dry‐out in fracture‐dominated geological reservoirs may alter the fracture space, impair rock absolute permeability, and cause a significant decrease in well injectivity. In this study, we numerically model the dry‐out processes occurring during supercritical CO2 (scCO2) injection into single brine‐filled fractures and evaluate the potential for salt precipitation under increasing effective normal stresses in the evaporative regime. We use an open‐source, parallel finite‐element framework to numerically model two‐phase flow through 2‐D fracture planes with aperture fields taken from naturally fractured granite cores at the Grimsel Test Site in Switzerland. Our results reveal a displacement front and a subsequent dry‐out front in all simulated scenarios, where higher effective stresses caused more flow channeling, higher rates of water evaporation, and larger volumes of salt precipitates. However, despite the larger salt volumes, the permeability impairment was lower at higher effective normal stresses. We conclude that the spatial distribution of the salt, precipitated in fractures with heterogeneous aperture fields, strongly affects the absolute permeability impairment caused by formation dry‐out. The numerical simulations assist in understanding the behavior of the injectivity in fractures and fracture networks during subsurface applications that involve scCO2 injection into brine.

Multiphase fluid flow through rock fractures occurs in many reservoir applications such as geological CO2 storage, Enhanced Geothermal Systems (EGS), nuclear waste disposal, and oil and gas production. However, constitutional relations of capillary pressure versus fluid saturation, particularly considering the change of fracture aperture distributions under various stress conditions, are poorly understood. In this study, we use fracture geometries of naturally-fractured granodiorite cores as input for numerical simulations of two-phase brine displacement by super critical CO2 under various effective normal stress conditions. The aperture fields are first mapped via photogrammetry, and the effective normal stresses are applied by means of a Fast Fourier Transform (FFT)-based convolution numerical method. Throughout the simulations, the capillary pressure is evaluated from the local aperture. Two approaches to obtain the capillary pressure are used for comparison: either directly using the Young-Laplace equation, or the van Genuchten equation fitted from capillary pressure-saturation relations generated using the pore-occupancy model. Analyses of the resulting CO2 injection patterns and the breakthrough times enable investigation of the relationships between the effective normal stress, flow channelling and aperturebased capillary pressures. The obtained results assist the evaluation of two-phase flow through fractures in the context of various subsurface applications.

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