Cyclic Thermal Shock‐Induced Permeability Enhancement in Tight Lithologies: Microstructural Controls and Elastic‐Wave Monitoring

Abstract

Enhanced geothermal systems rely on increasing permeability and pore surface area in rock. Cyclic thermal shocking can achieve both by inducing thermal cracks through repeated rapid cooling. Laboratory experiments subjected micritic limestone, granodiorite, and trachybasalt to up to 10 thermal shock cycles, while tracking crack evolution qualitatively using time‐lapse electron microscopy and quantifying pressure‐dependent permeability and elastic wave velocities. This work advances prior efforts focused primarily on crack initiation by demonstrating how lithology‐specific microstructures govern the cyclic evolution, persistence, and efficiency of pressure‐dependent permeability enhancement during cyclic thermal shocking. This reframes microstructure as a key design variable controlling permeability enhancement and monitoring during geothermal stimulation. Contrasting mineral thermal properties, large mineral grains, and irregular vugs promote the greatest permeability enhancement. Velocity reductions were most pronounced <10 MPa effective pressure (Peff) and diminished with increasing cycle number, indicating that velocity‐based monitoring in geothermal systems must account for Peff and cycle number.