The effect of temperature on the mechanical and hydraulic properties of sedimentary rocks

Abstract

The evaluation of the geomechanical and hydraulic properties of rocks under in situ conditions is essential for optimizing subsurface industrial operations. In this study, we investigate the impact of temperature on the hydraulic and mechanical properties of sandstone and carbonate rocks collected from southern Lebanon. The properties include the Unconfined Compressive Strength, Young's modulus, Poisson's ratio, compressional wave velocity, porosity, and permeability. Four distinct rock samples were examined: bioturbated limestone, bioturbated siliceous limestone, bioclastic intraclastic sandstone, and quartz arenite, which were analyzed through thin-sectioning and scanning electron microscopy. Mechanical properties were determined through uni-axial compression testing and ultrasonic measurements, while a gas permeameter and Helium porosimeter were employed for measuring permeability and porosity, respectively. In carbonate rocks, no significant changes in mechanical properties were observed with varying temperatures, whereas in sandstone samples, these properties decreased as temperature increased. The compressional wave velocity decreased for all rock types as temperature increased due to the formation of thermal cracks and the expansion of intra-granular pores. We note that the permeability initially decreased when temperature varied between 25°C and 85°C, which is attributed to the narrowing of pre-existing intergranular microcracks caused by thermal expansion of the porous solid matrix. However, permeability subsequently increased beyond 85°C as thermal cracks developed and created interconnected pathways. Porosity, however, increased continuously with temperature, influenced by both inter- and intra-granular pore space as well as the presence of cracks. The study suggests that with adequate implementations, rock properties can be improved for application in geothermal exploration and carbon storage.