Experimental and numerical geomechanical analysis of granite and marble degradation under thermal shock, acid treatment and thawing conditions

This study investigates the coupled effects of heat treatment, cryogenic thermal shock, chemical dissolution and thawing methods on the mechanical and physical properties of granite and marble in the context of enhanced geothermal reservoir stimulation. Samples were heat treated at 150°C and 300°C, cooled using liquid nitrogen (LN2), exposed to 3% hydrochloric (HCl), hydrofluoric (HF), oxalic and acetic acids and subsequently thawed using either room-temperature or microwave methods. Brazilian tensile tests were conducted, along with P-wave velocity, density and absorbed energy measurements to evaluate damage evolution. Results show that combined thermo-cryo-chemical treatment significantly weakens the rocks. Peak fracture load decreased by up to 43% for granite and 57.6% for marble, with maximum weakening observed at 300°C under HCl treatment with microwave thawing. Damage factors reached 0.43 for granite and 0.58 for marble. Among the acids, HCl produced the strongest weakening effect, followed by HF, oxalic and acetic acids. Marble exhibited higher sensitivity due to its carbonate-rich composition. Numerical simulations using COMSOL Multiphysics showed strong posterior agreement with experimental results (deviations <2.3%) and successfully captured stiffness degradation, peak load reduction and thermal-stress evolution. The model provides insight into microcrack initiation and propagation under coupled thermo-cryo-chemical processes.