Browsing by Author "Hsu, Shao-Yiu"

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Effects of liquid layers and distribution patterns on three-phase saturation and relative permeability relationships: a micromodel study
(2017-12-01)
Tsai, Jui-Pin
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Chang, Liang-Cheng
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Hsu, Shao-Yiu
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Shan, Hsin-Yu
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土木工程學系
In the current study, we used micromodel experiments to study three-phase fluid flow in porous media. In contrast to previous studies, we simultaneously observed and measured pore-scale fluid behavior and three-phase constitutive relationships with digital image acquisition/analysis, fluid pressure control, and permeability assays. Our results showed that the fluid layers significantly influenced pore-scale, three-phase fluid displacement as well as water relative permeability. At low water saturation, water relative permeability not only depended on water saturation but also on the distributions of air and diesel. The results also indicate that the relative permeability-saturation model proposed by Parker et al. (1987) could not completely describe the experimental data from our three-phase flow experiments because these models ignore the effects of phase distribution. A simple bundle-of-tubes model shows that the water relative permeability was proportional to the number of apparently continuous water paths before the critical stage in which no apparently continuous water flow path could be found. Our findings constitute additional information about the essential constitutive relationships involved in both the understanding and the modeling of three-phase flows in porous media.
Effects of the Grain Size on Dynamic Capillary Pressure and the Modified Green-Ampt Model for Infiltration
(2018-01-01)
Tsai, Yi-Zhih
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Liu, Yu-Tung
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Wang, Yung-Li
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Chang, Liang-Cheng
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Hsu, Shao-Yiu
Darcy-scale capillary pressure is traditionally assumed to be constant. By contrast, a considerable gap exists between the measured and equilibrium capillary pressures when the same moisture saturation is considered with a high flow rate, and this gap is called the dynamic effect on the capillary pressure. In this study, downward infiltration experiments of sand columns are performed to measure cumulative infiltration and to calculate the wetting front depth and wetting front velocity in sands with different grain sizes. We estimate the equilibrium capillary pressure head or suction head at the wetting front using both the classical Green-Ampt (GAM) and modified Green-Ampt (MGAM) models. The results show that the performance of MGAM in simulating downward infiltration is superior to that of GAM. Moreover, because GAM neglects the dynamic effect, it systematically underestimates the equilibrium suction head in our experiments. We also find that the model parameters (alpha) over cap and beta of MGAM are affected by the grain size of sands and porosity, and the dynamic effect of the capillary pressure increases with decreasing grain size and increasing porosity.
Using the Resistivity Imaging Method to Monitor the Dynamic Effects on the Vadose Zone During Pumping Tests at the Pengtsuo Site in Pingtung, Taiwan
(2016-02)
Chang, Ping-Yu
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Hsu, Shao-Yiu
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Chang, Liang-Cheng
;
Chen, Wen-Fu
;
Chen, Yu-Wen
We conducted a time-lapse monitoring study during a well-pumping test at the Pengtsuo site in Pingtung, Taiwan. Water-level gauges were installed in four wells (P1, W1, O1, and O2) at the Pengtsuo site with different screen depths for the observation. We designed the pumping test to be executed in three phases: the background, the stepwise-pumping, and the continuous-pumping phases. The survey line crossed the four wells so that a comparison would be possible between the resistivity measurements and the water-level records. The resistivity differences relative to the pre-pumping background show that electrical resistivity imaging (ERI) can resolve changes due to dewatering from pumping activity. The time-lapse resistivity images reveal that the maximum resistivity increase took place at the locations in the vadose zone instead of at the ground-water surface. The variation in the resistivity differences in the vadose zone correlated to the change in groundwater level in the stepwise phase. On the other hand, the resistivity-difference change was not fully consistent with the groundwater-level change in the continuous-pumping phase. We attribute the abnormal ERI signals to the dynamic non-equilibrium of the water movement in the vadose zone. The findings suggest that pumping designs can affect the changing resistivity differences and water-content distribution patterns. We show the potential of the ER method to reveal both the water flow and water-content changes in the vadose zone with different transient boundary conditions.