10:45 〜 12:15
[SCG58-P05] Transport properties of fluid at rock fractures generated by rapid decompression under hydrothermal conditions
キーワード：急減圧、断層、亀裂、浸透率
Fluid flow at a fault zone is crucial for understanding the mechanism of fault reactivation. In addition, it is possible that the fluid itself affects the permeability of the surrounding rock. High-temperature, high-pressure fluids in the fault zone can be rapidly decompressed due to the opening of jogs on faults during an earthquake. When fluid decompression occurs, surrounding rocks are cooled by the phase change of the fluid (i.e., flash vaporization). Although hydrothermal rapid decompression associated with the phase change of fluid could cause fracturing within the rock in the vicinity of the fault, the effect of fractures induced by hydrothermal rapid decompression on the permeability structure of the fault zone remains unclear. Here we conduct laboratory experiments of hydrothermal rapid decompression under high-temperature and high-pressure conditions.
The experiments were performed at temperatures of 400°C and 450°C on cylindrical-shaped granites (φ30 mm × h15 mm). Rock samples and distilled water are sealed inside the chamber, then the chamber is heated to create a hydrothermal environment inside. A thermocouple and pressure gauge record the temperature and pressure in the chamber. After heating to the target temperature, hydrothermal rapid decompression is generated by opening the valve connected to the inside of the chamber.
From the experimental results, the porosity of granite samples increased to 3.14 % at 550℃ by hydrothermal rapid decompression, which is significantly greater than that subjected to natural cooling. To clarify the distribution of fractures, X-ray computed tomography images were obtained from each sample. Microstructural observations show that the fractures occur and grow on surfaces that are in contact with water, indicating a clear heterogeneity in the fracture distribution induced by hydrothermal rapid decompression. In addition, permeability tended to approach asymptotically a specific value during repeated hydrothermal decompression. Therefore, hydrothermal rapid decompression associated with the phase change of water is expected to create an area of high fracture density in the vicinity of the surface in contact with the liquid phase, with little effect on the propagation of pre-existing fractures. To obtain a more detailed permeability structure of the fault zone induced by hydrothermal decompression associated with fault slip, a quantitative evaluation of fractures by microstructural observation of post-experimental samples is required.
The experiments were performed at temperatures of 400°C and 450°C on cylindrical-shaped granites (φ30 mm × h15 mm). Rock samples and distilled water are sealed inside the chamber, then the chamber is heated to create a hydrothermal environment inside. A thermocouple and pressure gauge record the temperature and pressure in the chamber. After heating to the target temperature, hydrothermal rapid decompression is generated by opening the valve connected to the inside of the chamber.
From the experimental results, the porosity of granite samples increased to 3.14 % at 550℃ by hydrothermal rapid decompression, which is significantly greater than that subjected to natural cooling. To clarify the distribution of fractures, X-ray computed tomography images were obtained from each sample. Microstructural observations show that the fractures occur and grow on surfaces that are in contact with water, indicating a clear heterogeneity in the fracture distribution induced by hydrothermal rapid decompression. In addition, permeability tended to approach asymptotically a specific value during repeated hydrothermal decompression. Therefore, hydrothermal rapid decompression associated with the phase change of water is expected to create an area of high fracture density in the vicinity of the surface in contact with the liquid phase, with little effect on the propagation of pre-existing fractures. To obtain a more detailed permeability structure of the fault zone induced by hydrothermal decompression associated with fault slip, a quantitative evaluation of fractures by microstructural observation of post-experimental samples is required.