17:15 〜 18:45
[AHW17-P12] DELINEATING PREFERENTIAL FRACTURE FLOW USING HIGH-PRECISION HEAT-PULSE FLOWMETER
The exploration of preferential groundwater flow in fractured rock constitutes a vital technique in hydrogeological research. In fractured rock, the intact rock is generally impermeable, and groundwater predominantly traverses a limited number of fractures serving as conduits. Nevertheless, the complexity of fracture distribution, marked by spatial heterogeneity and apertures and sizes, gives rise to intricate groundwater pathways. The actual flow paths in fractured rock are contingent upon the extent of fracture connectivity and whether they are filled.
Challenges in the characterization of preferential groundwater flow arise due to environmental constraints. Traditional approaches, such as double-packer tests, had assessed permeability in specific intervals of open holes but were limited by equipment precision, providing only average hydraulic conductivity values for larger sections of aquifers. Furthermore, the testing process is time-consuming, making it challenging to obtain continuous flow data along the borehole.
This study conducted a self-developed, high-precision heat-pulse flowmeter for preferential flow investigations of crystalline rock in Taiwan. The predominant lithology in this study was gneiss. The high-precision flowmeter utilized a multi-layered flow division device to temporarily mitigate the influence of adjacent up and down flow on the investigated segment. Due to the rubber composition and elasticity of the multi-layered system, there was no need for additional inflation. This not only saved testing time but also enabled continuous measurement data along the entire well. The heat-pulse test was conducted under high-pumping conditions (20 L/min) with a measurement interval of 10 cm to locate preferential flow fractures in a borehole and characterize the hydraulic conductivity of each fracture. This result revealed a poor correlation between the locations of permeable fractures and the high-density fracture zones. This outcome suggested that permeability cannot be solely determined based on the number of fractures. The high-precision heat-pulse could provide us with a better understanding of the actual flow dynamics of preferential flow paths in fractured rock formations. This novel technique serves as valuable references for applications in tunnel engineering, geothermal energy, pollutant transport, carbon dioxide sequestration, and related research areas.
Challenges in the characterization of preferential groundwater flow arise due to environmental constraints. Traditional approaches, such as double-packer tests, had assessed permeability in specific intervals of open holes but were limited by equipment precision, providing only average hydraulic conductivity values for larger sections of aquifers. Furthermore, the testing process is time-consuming, making it challenging to obtain continuous flow data along the borehole.
This study conducted a self-developed, high-precision heat-pulse flowmeter for preferential flow investigations of crystalline rock in Taiwan. The predominant lithology in this study was gneiss. The high-precision flowmeter utilized a multi-layered flow division device to temporarily mitigate the influence of adjacent up and down flow on the investigated segment. Due to the rubber composition and elasticity of the multi-layered system, there was no need for additional inflation. This not only saved testing time but also enabled continuous measurement data along the entire well. The heat-pulse test was conducted under high-pumping conditions (20 L/min) with a measurement interval of 10 cm to locate preferential flow fractures in a borehole and characterize the hydraulic conductivity of each fracture. This result revealed a poor correlation between the locations of permeable fractures and the high-density fracture zones. This outcome suggested that permeability cannot be solely determined based on the number of fractures. The high-precision heat-pulse could provide us with a better understanding of the actual flow dynamics of preferential flow paths in fractured rock formations. This novel technique serves as valuable references for applications in tunnel engineering, geothermal energy, pollutant transport, carbon dioxide sequestration, and related research areas.