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  • 1
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    Capillary pressure-saturation relations in quartz and carbonate sands: Limitations for correlating capillary and wettability influences on air, oil, and supercritical CO2 trapping (2016)
    Wiley
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    Publication Date: 2016-08-17
    Description: ABSTRACT Capillary pressure ( P c ) – saturation ( S w ) relations are essential for predicting equilibrium and flow of immiscible fluid pairs in soils and deeper geologic formations. In systems that are difficult to measure, behavior is often estimated based on capillary scaling of easily measured P c – S w relations (e.g., air-water, and oil-water), yet the reliability of such approximations needs to be examined. In this study, seventeen sets of brine drainage and imbibition curves were measured with air-brine, decane-brine, and supercritical (sc) CO 2 -brine in homogeneous quartz and carbonate sands, using porous plate systems under ambient (0.1 MPa, 23 ˚C) and reservoir (12.0 MPa, 45 ˚C) conditions. Comparisons between these measurements showed significant differences in residual nonwetting phase saturation, S nw, r . Through applying capillary scaling, changes in interfacial properties were indicated, particularly wettability. With respect to the residual trapping of the nonwetting phases, S nwr , CO2  〉  S nwr , decane  〉  S nwr , air . Decane-brine and scCO 2 -brine P c – S w curves deviated significantly from predictions assuming hydrophilic interactions. Moreover, neither the scaled capillary behavior nor S nw, r for scCO 2 -brine were well represented by decane-brine, apparently because of differences in wettability and viscosities, indicating limitations for using decane (and other organic liquids) as a surrogate fluid in studies intended to apply to geological carbon sequestration. Thus, challenges remain in applying scaling for predicting capillary trapping and multiphase displacement processes across such diverse fields as vadose zone hydrology, enhanced oil recovery, and geologic carbon sequestration. This article is protected by copyright. All rights reserved.
    Print ISSN: 0043-1397
    Electronic ISSN: 1944-7973
    Topics: Architecture, Civil Engineering, Surveying , Geography
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 2
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    Wettability impact on supercritical CO2 capillary trapping: Pore-scale visualization and quantification (2017)
    Wiley
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    Publication Date: 2017-07-14
    Description: How the wettability of pore surfaces affects supercritical (sc) CO 2 capillary trapping in geologic carbon sequestration (GCS) is not well understood, and available evidence appears inconsistent. Using a high-pressure micromodel-microscopy system with image analysis, we studied the impact of wettability on scCO 2 capillary trapping during short-term brine flooding (80 seconds, 8 to 667 pore volumes). Experiments on brine displacing scCO 2 were conducted at 8.5 MPa and 45°C in water-wet (static contact angle θ  = 20° ± 8°) and intermediate-wet ( θ  = 94° ± 13°) homogeneous micromodels under four different flow rates (capillary number Ca ranging from 9 × 10 −6 to 8 × 10 −4 ) with a total of eight conditions (four replicates for each). Brine invasion processes were recorded and statistical analysis was performed for over two thousand images of scCO 2 saturations, and scCO 2 cluster characteristics. The trapped scCO 2 saturation under intermediate-wet conditions is 15% higher than under water-wet conditions under the slowest flow rate ( Ca ∼ 9 × 10 −6 ). Based on the visualization and scCO 2 cluster analyses, we show that the scCO 2 trapping process in our micromodels is governed by bypass trapping that is enhanced by the larger contact angle. Smaller contact angles enhance cooperative pore filling and widen brine fingers (or channels), leading to smaller volumes of scCO 2 being bypassed. Increased flow rates suppress this wettability effect.
    Print ISSN: 0043-1397
    Electronic ISSN: 1944-7973
    Topics: Architecture, Civil Engineering, Surveying , Geography
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  • 3
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    Wettability and flow rate impacts on immiscible displacement: A theoretical model (2018)
    Wiley
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    Publication Date: 2018-03-06
    Description: When a more viscous fluid displaces a less viscous one in porous media, viscous pressure drop stabilizes the displacement front against capillary pressure fluctuation. For this favorable viscous ratio conditions, previous studies focused on the front instability under slow flow conditions but did not address competing effects of wettability and flow rate. Here we study how this competition controls displacement patterns. We propose a theoretical model that describes the crossover from fingering to stable flow as a function of invading fluid contact angle θ and capillary number C a . The phase diagram predicted by the model shows that decreasing θ stabilizes the displacement for θ ≥45 ∘ and the critical contact angle θ c increases with C a . The boundary between corner flow and cooperative filling for θ 〈 45 ∘ is also described. This work extends the classic phase diagram, and has potential applications in predicting CO 2 capillary trapping and manipulating wettability to enhance gas/oil displacement efficiency.
    Print ISSN: 0094-8276
    Electronic ISSN: 1944-8007
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 4
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    Water Saturation Relations and Their Diffusion-Limited Equilibration in Gas Shale: Implications for Gas Flow in Unconventional Reservoirs (2017)
    Wiley
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    Publication Date: 2017-11-16
    Description: Large volumes of water are used for hydraulic fracturing of low permeability shale reservoirs to stimulate gas production, with most of the water remaining unrecovered and distributed in a poorly understood manner within stimulated regions. Because water partitioning into shale pores controls gas release, we measured the water saturation dependence on relative humidity ( rh ) and capillary pressure ( P c ) for imbibition (adsorption) as well as drainage (desorption) on samples of Woodford Shale. Experiments and modeling of water vapor adsorption into shale laminae at rh = 0.31 demonstrated that long times are needed to characterize equilibrium in larger (5 mm thick) pieces of shales, and yielded effective diffusion coefficients from 9 × 10 −9 to 3 × 10 −8 m 2 s −1 , similar in magnitude to the literature values for typical low porosity and low permeability rocks. Most of the experiments, conducted at 50 ˚C on crushed shale grains in order to facilitate rapid equilibration, showed significant saturation hysteresis, and that very large P c (∼1 MPa) are required to drain the shales. These results quantify the severity of the water blocking problem, and suggest that gas production from unconventional reservoirs is largely associated with stimulated regions that have had little or no exposure to injected water. Gravity drainage of water from fractures residing above horizontal wells reconciles gas production in the presence of largely unrecovered injected water, and is discussed in the broader context of unsaturated flow in fractures.
    Print ISSN: 0043-1397
    Electronic ISSN: 1944-7973
    Topics: Architecture, Civil Engineering, Surveying , Geography
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  • 5
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    Consolidation of undoped, monoclinic zirconia polycrystals by flash-sintering (2017)
    Wiley
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    Publication Date: 2017-05-03
    Description: Consolidated, monoclinic ZrO 2 polycrystal was produced from undoped ZrO 2 powders in air by flash-sintering at the sintering temperature of 1350°C for 5 min or 3 hours under an applied DC electric field of 175 V/cm. When the ZrO 2 was heated under the applied DC field, the electric current of the specimen steeply increased at the furnace temperature of 1335°C below the sintering temperature of 1350°C. When the furnace temperature was decreased from the sintering temperature of 1350°C to room temperature, volumetric expansion associated with tetragonal to monoclinic phase transformation gradually took place at the furnace temperature from 1000°C to 750°C, and monoclinic ZrO 2 body was remained consolidated even at room temperature in both specimen. In contrast, conventionally-sintered ZrO 2 without applying DC field exhibited the abrupt volumetric expansion at about 1000°C, and shattered. SEM observation revealed the presence of grain boundary second phase in the flash-sintered specimen for 3 hours, which is a possible origin of keeping a bulk body at room temperature. The thinner second phase is considered to be formed also in the flash-sintered specimen for 5min. although the formation of the phase could not be observed clearly by SEM observation. On the other hand, XRD measurements showed that ‹001› directions of the monoclinic ZrO 2 grains were oriented along the applied DC field after the isothermal flash-sintering for 3 hours while the grain alignment could not be observed in flash-sintered specimen for 5min. The alignment of ZrO 2 grains observed in the isothermal flash-sintering is considered to be closely related to the preferential direction of oxygen ionic conduction and the second phase formed along grain boundaries. This article is protected by copyright. All rights reserved.
    Print ISSN: 0002-7820
    Electronic ISSN: 1551-2916
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
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  • 6
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    Electric-current-controlled synthesis of BaTiO3 (2017)
    Wiley
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    Publication Date: 2017-04-22
    Description: In BaTiO 3 , flash sintering associated with a surge of the specimen electric current sometimes results in an inhomogeneous microstructure including Ti-excess secondary phases because of discharging. We applied field assisted sintering technique (FAST) under precisely controlled specimen current, that was set just below the threshold value for the occurrence of flash event for BaTiO 3 , to avoid the occurrence of the discharging. As a result, uniform and fine-grained compacts were obtained without any secondary phases. A relative density of approximately 92% was achieved under FAST condition of 100 V/cm with a limiting current of 72mA and soaking time of 3h at 1070 °C. The voltages during sintering under a constant current of 72mA were found to decrease during the soaking process. Electron energy loss spectroscopy revealed the generation of excess oxygen vacancies at/near grain boundaries. The excess oxygen vacancies induced by application of DC electric fields were confirmed to reduce the voltages and to retard the shrinkage rate in a final sintering stage. This article is protected by copyright. All rights reserved.
    Print ISSN: 0002-7820
    Electronic ISSN: 1551-2916
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
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  • 7
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    Intergranular amorphous films formed by DC electric field in pure zirconia (2018)
    Wiley
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    Publication Date: 2018-02-11
    Description: It is difficult to obtain pure ZrO 2 sintered compacts with a bulk style at room temperature because a large volumetric expansion from tetragonal to monoclinic phase ( t / m ) transformation occurs at around 1000 °C, which is lower than the sintering temperature. In contrast, pure monoclinic ZrO 2 can be consolidated without shattering by using flash-sintering at 1350 °C for 5 min under an applied DC electric field of 175 V/cm. High-resolution transmission electron microscopy and electron energy loss spectroscopy have revealed that amorphous films are formed along grain boundaries after flash-sintering at 1350 °C for 5 min. Monoclinic ZrO 2 flash-sintered compact including the amorphous films are able to survive without shattering through the t / m transformation, as the amorphous films partially absorb the large volumetric expansion arising from the t / m transformation. The formation of the amorphous films results from the severe reducing condition due to the applied DC electric fields during flash-sintering. This article is protected by copyright. All rights reserved.
    Print ISSN: 0002-7820
    Electronic ISSN: 1551-2916
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
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  • 8
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    Future risks of tsunami‐induced seawater intrusion into unconfined coastal aquifers: insights from numerical simulations at Niijima Island, Japan (2019)
    Wiley
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    Publication Date: 2019
    Description: Abstract Tsunami‐induced seawater inundation causes vertical seawater infiltration into coastal aquifers and induces unexpected salinization of fresh groundwater resources. Assessing future risks of seawater intrusion in tsunami‐prone areas can provide essential information supporting disaster preparedness. In this study, we investigated seawater intrusion and aquifer recovery processes under the future Nankai earthquake and tsunami scenarios at Niijima Island, Japan. A groundwater model with a 2‐D vertical cross‐section was developed to solve variable‐density flow and salt transport in unsaturated‐saturated media using the numerical code, FEFLOW. Our simulation results indicate that the unsaturated zone behaves as an initial storage of the infiltrated seawater and controls the maximum amount of seawater infiltration during the anticipated tsunami inundation. The bedrock structures affect the direction of seawater movement in the saturated zone and the flushing time of the polluted aquifer. Our analysis suggests that the tsunami inundation height, the rainfall recharge rate, and hydraulic conductivity are the primary sources of uncertainties in the simulation results. These findings have implications for other tsunami‐prone zones with respect to the understanding of the relevant physical processes and model uncertainties.
    Print ISSN: 0043-1397
    Electronic ISSN: 1944-7973
    Topics: Architecture, Civil Engineering, Surveying , Geography
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 9
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    Depth‐ and Time‐Resolved Distributions of Snowmelt‐Driven Hillslope Subsurface Flow and Transport and Their Contributions to Surface Waters (2019)
    Wiley
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    Publication Date: 2019
    Description: Abstract Major components of hydrologic and elemental cycles reside underground, where their complex dynamics and linkages to surface waters are obscure. We delineated seasonal subsurface flow and transport dynamics along a hillslope in the Rocky Mountains (USA), where precipitation occurs primarily as winter snow and drainage discharges into the East River, a tributary of the Gunnison River. Hydraulic and geochemical measurements down to 10 m below ground surface supported application of transmissivity feedback of snowmelt to describe subsurface flow and transport through three zones: soil, weathering shale, and saturated fractured shale. Groundwater flow is predicted to depths of at least 176 m, although a shallower limit exists if hillslope‐scale hydraulic conductivities are higher than our local measurements. Snowmelt during the high snowpack water year 2017 sustained flow along the weathering zone and downslope within the soil, while negligible downslope flow occurred along the soil during the low snowpack water year 2018. We introduce subsurface concentration‐discharge (C‐Q) relations for explaining hillslope contributions to C‐Q observed in rivers and demonstrate their calculations based on transmissivity fluxes and measured pore water specific conductance and dissolved organic carbon. The specific conductance data show that major ions in the hillslope pore waters, primarily from the weathering and fractured shale, are about six times more concentrated than in the river, indicating hillslope solute loads are disproportionately high, while flow from this site and similar regions are relatively smaller. This methodology is applicable in different representative environments within snow‐dominated watersheds for linking their subsurface exports to surface waters.
    Print ISSN: 0043-1397
    Electronic ISSN: 1944-7973
    Topics: Architecture, Civil Engineering, Surveying , Geography
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  • 10
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    Genetic Structure and Speciation of Zoysiagrass Ecotypes Collected in Japan (2016)
    Wiley
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    Publication Date: 2016-03-01
    Print ISSN: 0011-183X
    Electronic ISSN: 1435-0653
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
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