Mechanical Properties of High-Temperature Granite under Liquid Nitrogen Cooling

Abstract

The cooling characteristics of liquid nitrogen can effectively weaken the mechanical properties of dry hot rock reservoirs, improve the porosity and permeability of dry hot rock, and thus improve the development and utilization of geothermal resources. In order to explore the weakening effect of liquid nitrogen cooling characteristics on high-temperature reservoir rocks, uniaxial compression tests, Brazil splitting tests, and three-point bending tests were conducted on high-temperature granite, and synchronous acoustic emission tests were conducted to monitor the damage evolution of rocks. It is found that under the action of liquid nitrogen, the elastic modulus, peak strength, fracture toughness, and other mechanical properties of granite decrease to varying degrees. At different initial temperatures, the damage degree of liquid nitrogen to granite is different. The higher the initial temperature of granite, the greater the damage effect of liquid nitrogen on granite. The low-temperature characteristics of liquid nitrogen not only have the effect of cracking damage on granite but also have the effect of thermal stress on granite. If the temperature difference between the two is large, the heat released in the combination process will be higher. The greater the temperature difference, the greater the damage to granite. Under the action of liquid nitrogen, the acoustic emission characteristics of granite also show different evolution laws, and the ringing count of rock increases significantly, which indicates that liquid nitrogen aggravates the internal damage of granite, making the rock more fractured during fracturing. The research results can provide some scientific guidance for the development and utilization of geothermal energy.

Experimental Study on Mode I Fracture Characteristics of Granite after Low Temperature Cooling with Liquid Nitrogen

“…In terms of rock fracture toughness, Yin et al [23] discovered that the fracture toughness of granite significantly decreased with an increase in the number of heating and liquid nitrogen cooling cycles. Thermal shock, thermal stress, and fatigue damage are the main factors contributing to the continuous deterioration of rock mechanical properties [24]. Shao et al [25] reached a similar conclusion through a three-point bending test on granite cooled with liquid nitrogen and also emphasized the influence of the initial temperature of the granite on mode I fracture characteristics.…”

Migration mechanism of grouting slurry and permeability reduction in mining fractured rock mass

“…According to the above equation, the ratio of the permeability of the fractured rock sample to the initial permeability can be obtained by solving S and C . According to the classical particle migration-deposition model 23 – 26 , the relationship between the concentration of deposited particles C and the concentration of suspended particles S can be established. where ρ b is the dry volume density of fractured rock mass; ρ s ’ is the particle density of fractured rock mass.…”

Effect of weakening characteristics of mechanical properties of granite under the action of liquid nitrogen

“…Nitrogen gas itself is colorless and odorless, belonging to inert gases, and does not cause pollution to the environment. Against this engineering backdrop, exploring the cooling treatment of high-temperature rocks using liquid nitrogen serves as a vital foundation for the application of waterless fracturing in oil and gas extraction, geothermal resource development, and deep rock mechanics studies (Wang et al, 2023;Xue et al, 2023b). Furthermore, this study's sequence of experiments and numerical calculations elucidates the potential application of nitrogen-induced fracturing in EGS development, offering guidance and technical parameters for nitrogen-induced fracturing in geothermal development.…”