Experimental Study of Permeability and Clay Mineral Staged Changes in Siltstone at High Temperatures

Current studies on siltstone permeability at high temperatures are limited to below 800 °C, which cannot direct underground engineering projects with higher temperatures. This study conducts general thermal simulations up to 1400 °C and investigates the permeability and mineral changes of siltstone with temperature. The results show that the permeability and pore structure changes can be divided into 3 stages, and the clay mineral changes lead to stage division. The dehydroxylation leads to increased permeability at Stage II, and recrystallization after liquid phase cooling leads to complex changes in permeability and pore structure at Stage III. The permeability of Mg-containing siltstone after an above 1000 °C treatment has a stronger temperature response due to the high liquid phase content and the formation of cordierite. The suitability of magnesium-containing rocks in underground engineering projects must be considered carefully.