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Hydraulic properties of stressed granite fractures with heat-induced void alteration
Abstract During the extraction of geothermal heat, the changes in temperature and pressure environments can alter the mechanical and hydraulic behavior of fractured rock masses, affecting the overall transmissivity and heat extraction efficiency accordingly. This study carried out a series of experiments, including X-ray diffraction (XRD), scanning electron microscope (SEM), uniaxial compression tests, and surface morphological scanning, to explore the influence of reservoir temperature on the mechanical behavior of granite and fracture surface topography. The results indicate that as the temperature increases, the uniaxial compressive strength, elastic modulus, and Poisson's ratio of granite show similar variation patterns that increase as the temperature approaches 200 °C and then decrease. In addition, with the increase in temperature, the overall surface elevation and roughness parameters generally decrease due to surface asperity degradation, with the maximum mean mechanical aperture found at 200 °C. Flow simulations were conducted to further explore the influence of temperature and pressure environments on fracture transmissivity and flow fields. It is found that the normalized equivalent hydraulic aperture B N of the tested fractures decreases progressively as the stress increases, and more scattered distributions of B N are observed under higher compressive stresses. Moreover, with the continuous increase in temperature, the average B N slowly increases to its peak of ~0.78 at 200 °C, then it decreases to ~0.76 at 300 °C and remains nearly constant. These findings can be important for assessing heat production performances during the geothermal extraction process with spatially and temporally varying reservoir temperatures and pressures.
Highlights Temperature and pressure effect on granite properties are analyzed. Surface roughness decreases due to heat-induced asperity degradation. UCS and transmissivity reach their maximum at 200 °C with increasing temperature.
Hydraulic properties of stressed granite fractures with heat-induced void alteration
Abstract During the extraction of geothermal heat, the changes in temperature and pressure environments can alter the mechanical and hydraulic behavior of fractured rock masses, affecting the overall transmissivity and heat extraction efficiency accordingly. This study carried out a series of experiments, including X-ray diffraction (XRD), scanning electron microscope (SEM), uniaxial compression tests, and surface morphological scanning, to explore the influence of reservoir temperature on the mechanical behavior of granite and fracture surface topography. The results indicate that as the temperature increases, the uniaxial compressive strength, elastic modulus, and Poisson's ratio of granite show similar variation patterns that increase as the temperature approaches 200 °C and then decrease. In addition, with the increase in temperature, the overall surface elevation and roughness parameters generally decrease due to surface asperity degradation, with the maximum mean mechanical aperture found at 200 °C. Flow simulations were conducted to further explore the influence of temperature and pressure environments on fracture transmissivity and flow fields. It is found that the normalized equivalent hydraulic aperture B N of the tested fractures decreases progressively as the stress increases, and more scattered distributions of B N are observed under higher compressive stresses. Moreover, with the continuous increase in temperature, the average B N slowly increases to its peak of ~0.78 at 200 °C, then it decreases to ~0.76 at 300 °C and remains nearly constant. These findings can be important for assessing heat production performances during the geothermal extraction process with spatially and temporally varying reservoir temperatures and pressures.
Highlights Temperature and pressure effect on granite properties are analyzed. Surface roughness decreases due to heat-induced asperity degradation. UCS and transmissivity reach their maximum at 200 °C with increasing temperature.
Hydraulic properties of stressed granite fractures with heat-induced void alteration
Wang, Fei (author) / Xie, Heping (author) / Li, Cunbao (author) / Li, Minghui (author) / Long, Xiting (author) / Shan, Ke (author) / Wang, Zhihe (author)
Engineering Geology ; 333
2024-03-11
Article (Journal)
Electronic Resource
English
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