ABSTRACT:

Geothermal energy is a renewable energy resource that can be found in abundance on the earth. Effective fracturing technology is the precondition to develop it efficiently. In this paper, the tests of the P-wave velocity, uniaxial compressive strength, and permeability of the granite after high temperature treated with air cooling and liquid nitrogen cooling were conducted. The variations of the P-wave velocity, uniaxial compressive strength, and permeability of the granite after treatment were obtained. Results indicate that the p-wave, uniaxial compressive strength, and Young's modulus decreased after the treatment, while the permeability increased. The p-wave and permeability are positively correlated with the treatment temperature. The scanning electron microscope (SEM) and x-ray diffraction (XRD) were employed to observe the microstructure and mineral content of the granite, respectively. Many micro-cracks were produced after liquid nitrogen treatment. All the experimental results indicate that liquid nitrogen cooling can induce significant thermal stress and has a positive impact on rock failure. It is expected to provide some guidance for the application of liquid nitrogen fracturing in geothermal reservoirs, especially in hot dry rock reservoirs.

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