Experimental Study on the Effect of Thermal Shock on Physical and Mechanical Properties of Limestone

Abstract

Thermal shock is the physical process of rapid cooling of a hot object. The physical and mechanical properties of rocks that have undergone thermal shock will change. This variation can be applied to the development of geothermal in limestone reservoirs and serve as an effective means of enhancing heat exchange capacity. The essence of this is rock thermal shock rupture. The reason for the change in rock properties due to thermal shock is distinguished from other factors and is a process of instantaneous impact thermal stress caused by non-constant heat transfer, resulting in rock damage from microscopic damage to macroscopic damage. In order to study the variation of physical and mechanical properties of limestone with heating and cooling temperatures under the effect of thermal shock, a self-developed thermal shock test device was used to test the physical and mechanical properties of limestone heated to 100 °C~600 °C after thermal shock. The results strongly suggest that the heating temperature under the effect of thermal shock is the main factor affecting the evolution of basic physical properties of limestone; with the increase in heating temperature, the color of the specimen changes from off-white to white, the mass decreases and the volume nonlinearly increases, with a maximum reduction of 1.39% in mass and a maximum expansion of 2.79% in volume at 600 °C. Indeed, 500 °C is the temperature of abrupt mass loss. The heating temperature and the cooling medium temperature act together to deteriorate the mechanical properties of limestone. With increasing heating temperature (decreasing cooling temperature), the uniaxial compressive strength of limestone decreased by 39.5% (19.3%), modulus of elasticity by 59.5% (22.9%), tensile strength by 42.9% (7.6%), and cohesion by 43.2% (22.5%). The peak strain increases by 74.2% and the angle of internal friction increases by 27% (25.9%). The above data are average values. The empirical equations of the compressive strength, modulus of elasticity, tensile strength of limestone under the action of thermal shock versus heating temperature were obtained. The differences in the physical and mechanical properties of limestone after two heat treatments (thermal shock and high-temperature heating) were compared and analyzed, and the results showed that the physical and mechanical properties of limestone deteriorated more severely after thermal shock compared to high-temperature heating. The research results can provide technical support for the drilling of geothermal development and wellbore stability assessment in limestone reservoirs, and enrich the theory of high-temperature rock mechanics.