Experimental Investigation of the Damage Characteristics of High-Temperature Granite Subjected to Liquid Nitrogen Treatment

Experimental study on the breakdown mechanism of high temperature granite induced by liquid nitrogen fracturing: An implication to geothermal reservoirs

“…During fracturing, the breakdown pressure is controlled by both the mechanical properties of rock and the stress status of reservoir. As described in our previous study, the tensile strength and stress field of high temperature rock were greatly changed due to the injection of cryogenic LN [ 46 , 56 ]. In order to predict the breakdown pressure of hydraulic fracturing, a new model was proposed by modifying the traditional Hubbert-Willis criterion [ 60 ].…”

“…To better analyze the influences of heating, LN cooling and cryogenic condition on the damage of granite, we performed the ultrasonic tests on these samples, respective in previous investigation [ 46 ]. The propagation of ultrasonic waves depends on the damage of rock closely.…”

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Fig. 4 The effect of heating and LN treatment on ultrasonic velocity of granite [ 46 ]. The decreased ultrasonic velocity indicated the growth of damage and microcracks.

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Study on Damage Characteristics of Hot Dry Rock by Liquid Nitrogen Cyclic Cold Shocks Based on Ultrasonic Testing

“…In recent years, numerous studies have been conducted by scholars on the damage and destruction characteristics of liquid nitrogen cold shock on high-temperature granite. Cai et al 30 performed ultrasonic, Brazilian splitting and acoustic emission (AE) tests on high-temperature granite before and after liquid nitrogen treatment. They found that liquid nitrogen cold shock causes additional low-temperature damage to high-temperature granite, but the extent of damage caused by liquid nitrogen cold shock is different under different heating temperatures.…”

“…For example, Li et al 28 defined the damage coefficient of granite after supercritical CO 2 treatment through ultrasonic wave velocity, and the results showed that the damage coefficient of granite developed rapidly in the initial stage of supercritical CO 2 saturation and remained stable with the increase of saturation time. Cai et al 30 conducted ultrasonic testing on hightemperature granite before and after liquid nitrogen treatment and found that when the heating temperature was higher than 300 °C, the decreased amplitude of ultrasonic wave velocity diminished with the increase of heating temperature, which was much lower than that caused by heating. Pan et al 9 performed ultrasonic testing on granite under different heating temperatures and chemical solution treatment conditions and found that the P-wave decreased linearly with the increase of heating temperature, and the thermal conductivity and thermal diffusivity were positively correlated with the P-wave velocity.…”