A numerical study on the long term thermo-poroelastic effects of cold water injection into naturally fractured geothermal reservoirs     

Joshua Koh  Hamid RoshanSheik S. Rahman 《Computers and Geotechnics》2011

The residing fracture system and the prevailing in situ stresses have a significant impact on fluid flow and heat transfer in crystalline rocks. The long term response of fracture systems to changes in effective stresses, in particular the long term geo-mechanical effects of thermal stresses on reservoir characteristics is of particular interest to the geothermal industry.  相似文献   

Delineation of recharge patterns and contaminant transport using 3H–3He in a shallow aquifer contaminated by chlorinated solvents in South Korea     

Dugin Kaown  Dong-Chan Koh  D. Kip Solomon  Yoon-Yeol Yoon  Jaeha Yang  Kang-Kun Lee 《Hydrogeology Journal》2014,22(5):1041-1054

Stable isotopes of water and ³H–³He were used to delineate recharge patterns and contaminant transport for a granitic regolith aquifer in an industrial complex in Wonju, South Korea, that has historically been contaminated with chlorinated solvents including trichloroethene (TCE) and carbon tetrachloride (CT). Groundwater recharge mainly occurred in upgradient forested areas while little recharge occurred in the downgradient industrial areas covered with extensive sections of impermeable pavement and paddy fields. δ¹⁸O and δD data indicated that groundwater was mainly derived from summer precipitation. The apparent groundwater ages using ³H–³He ranged from 1 to 4 yrs in the upgradient area and from 9 to 10 yrs in the downgradient area. Comparison of groundwater flow velocities based on Darcy’s law and those calculated with simple mass balance models and groundwater age supported the presence of preferential pathways for TCE movement in the study area. Measureable TCE was observed in groundwater irrespective of groundwater age. Considering the 3-yr duration of the TCE spill, 14 yrs before sampling, this indicates that TCE plumes were continuously fed from sources in the unsaturated zone after the spill ended and moved downgradient without significant degradation in the aquifer.  相似文献   

Assessing sustainability of groundwater resources on Jeju Island,South Korea,under climate change,drought, and increased usage   总被引：2，自引：0，他引：2  

Aly I. El-Kadi  Suzanne Tillery  Robert B. Whittier  Benjamin Hagedorn  Alan Mair  Kyoochul Ha  Gi-Won Koh 《Hydrogeology Journal》2014,22(3):625-642

Numerical groundwater models were used to assess groundwater sustainability on Jeju Island, South Korea, for various climate and groundwater withdrawal scenarios. Sustainability criteria included groundwater-level elevation, spring flows, and salinity. The latter was studied for the eastern sector of the island where saltwater intrusion is significant. Model results suggest that there is a need to revise the current estimate of sustainable yield of 1.77?×?10⁶ m³/day. At the maximum extraction of 84  % of the sustainable yield, a 10-year drought scenario would decrease spring flows by 28 %, dry up 27 % of springs, and decrease hydraulic head by an island-wide average of 7 m. Head values are particularly sensitive to changes in recharge in the western parts of the island, due to the relatively low hydraulic conductivity of fractured volcanic aquifers and increased groundwater extraction for irrigation. Increases in salinity are highest under drought conditions around the current 2-m head contour line, with an estimated increase of up to 9 g/L under 100 % sustainable-yield use. The study lists recommendations towards improving the island’s management of potable groundwater resources. However, results should be treated with caution given the available data limitations and the simplifying assumptions of the numerical modeling approaches.  相似文献   

Application of multiple-isotope and groundwater-age data to identify factors affecting the extent of denitrification in a shallow aquifer near a river in South Korea     

Dugin Kaown  Eun-Hee Koh  Bernhard Mayer  Heejung Kim  Dong Kyu Park  Byeong-Hak Park  Kang-Kun Lee 《Hydrogeology Journal》2018,26(6):2009-2020

The extent of denitrification in a small agricultural area near a river in Yangpyeong, South Korea, was determined using multiple isotopes, groundwater age, and physicochemical data for groundwater. The shallow groundwater at one monitoring site had high concentrations of NO₃-N (74–83 mg L^?1). The δ¹⁵N-NO₃ values for groundwater in the study area ranged between +9.1 and +24.6‰ in June 2014 and +12.2 to +21.6‰ in October 2014. High δ¹⁵N-NO₃ values (+10.7 to +12.5‰) in both sampling periods indicated that the high concentrations of nitrate in the groundwater originated from application of organic fertilizers and manure. In the northern part of the study area, some groundwater samples showed elevated δ¹⁵N-NO₃ and δ¹⁸O-NO₃ values, which suggest that nitrate was removed from the groundwater via denitrification, with N isotope enrichment factors ranging between ?4.8 and ?7.9‰ and O isotope enrichment factors varying between ?3.8 and ?4.9‰. Similar δD and δ¹⁸O values of the surface water and groundwater in the south appear to indicate that groundwater in that area was affected by surface-water infiltration. The mean residence times (MRTs) of groundwater showed younger ages in the south (10–20 years) than in the north (20–30 years). Hence, it was concluded that denitrification processes under anaerobic conditions with longer groundwater MRT in the northern part of the study area removed considerable amounts of nitrate. This study demonstrates that multi-isotope data combined with physicochemical data and age-dating information can be effectively applied to characterize nitrate contaminant sources and attenuation processes.  相似文献   

Oxygen penetration through invertebrate burrow walls in Korean tidal flat     

Bon Joo Koo  Chul-Hwan Koh 《Ocean Science Journal》2013,48(4):329-338

Macrofaunal burrows increase the surface area of the sediment-water interface, which has a great impact on the metabolism of aerobic microbes and the oscillation of reduced metabolites within the sediment. Given the importance of macrofauna in surficial sediments, the aim of this study is to examine the effects of burrow architectures on dissolved oxygen diffusion rates in comparison with unburrowed sediment, and thereby to evaluate the theoretical assumption used for modeling solute distribution in the burrow system using field samples. Employing microsensors, horizontal oxygen profiles were measured on a micrometer scale around burrows of seven invertebrates in tidal flats of the west coast of Korea. Oxygen diffusion distance through the burrow walls of seven invertebrates showed spatio-temporal variation with a range of 0.6 to 2.9 mm. Two groups of burrows were identified based on their oxygen diffusive properties relative to unburrowed sediments: 1) oxygen penetration similar to that of ambient sediments and 2) clearly enhanced oxygen penetration. Differences in the diffusive properties of the burrow wall were related to the burrow depth and diameter, existence of mucus lining on the wall, sediment grain size, and tidal phases. Also inhabitant activity was an important factor affecting oxygen penetration, which is discussed in the paper. These results further demonstrate that simplified assumptions (i.e. burrow structures are viewed as direct biogeochemical extensions of the sediment-water interface) may not be exact representation of the nature.  相似文献   

Influence of Pressure Change During Hydraulic Tests on Fracture Aperture     

Sung‐Hoon Ji  Yong‐Kwon Koh  Kristopher L. Kuhlman  Moo Yul Lee  Jong Won Choi 《Ground water》2013,51(2):298-304

In a series of field experiments, we evaluate the influence of a small water pressure change on fracture aperture during a hydraulic test. An experimental borehole is instrumented at the Korea Atomic Energy Research Institute (KAERI) Underground Research Tunnel (KURT). The target fracture for testing was found from the analyses of borehole logging and hydraulic tests. A double packer system was developed and installed in the test borehole to directly observe the aperture change due to water pressure change. Using this packer system, both aperture and flow rate are directly observed under various water pressures. Results indicate a slight change in fracture hydraulic head leads to an observable change in aperture. This suggests that aperture change should be considered when analyzing hydraulic test data from a sparsely fractured rock aquifer.  相似文献   

Mineralization Characteristics and Structural Controls of Hydrothermal Deposits in the Gyeongsang Basin, South Korea   总被引：1，自引：0，他引：1  

Sang-Mo  Koh  Chung-Ryul Ryoo  Min-Sub Song 《Resource Geology》2003,53(3):175-192

Abstract. Hydrothermal deposits in the Gyeongsang Basin show the genetic relationship with igneous activity from Late Cretaceous to Early Tertiary in the spatial and temporal viewpoints. Many hydrothermal Au-Ag-Cu-Pb-Zn and clay deposits are dominantly distributed within the Gyeongsang Basin. The Gyeongsang Basin is divided into seven metallogenic provinces by spatial distribution. The age ranges of igneous activity and mineralization are 140∼40 Ma and 100∼40 Ma, respectively, and the most dominant age ranges of the both activities are from 90 Ma (Coniacian) to 50 Ma (Eocene). The age consistency between igneous activity and mineralization suggests that this age range is the climactic period of the hydrothermal activity of the Gyeongsang Basin. The metallogenic epochs in the Gyeongsang Basin are divided into three epochs of 100∼80 Ma (western part of the Gyeongsang Basin), 80∼60 Ma (central part of the Gyeongsang Basin), and 60∼40 Ma (eastern part of the Gyeongsang Basin). The mineralization and igneous activity tend to become young eastward in the Gyeongsang Basin.
NNW-SSE mineralized veins from 100 to 80 Ma in the western part of the Gyeongsang Basin are interpreted as the control of the parallel tensional fissures caused by NNW-SSE compressional stress. NW-SE mineralized veins from 80 to 60 Ma in the central part of the Gyeongsang Basin seem to have been formed under the same stress as that of the Gaeum and Yangsan Fault Systems. Namely, NW-SE tensional stress is associated with a conjugate set of fracturing of the WNW-ESE Gaeum Fault System and NNE-SSW Yangsan Fault System. Also NE-SW mineralized veins from 60 to 40 Ma in the eastern part of the Gyeongsang Basin seem to be controlled by the NE-SW fractures. The fractures are related with NE-SW compressional stress and are developed as secondary fractures within the dextral strike slip Yangsan Fault System.  相似文献   

Compressional wave velocity of granite and amphibolite up to melting temperatures at 1 GPa   总被引：2，自引：0，他引：2  

Yoshitaka Aizawa  Kazuhiko Ito  Yoshiyuki Tatsumi 《Tectonophysics》2002,351(3):4108

Compressional wave velocities (V_P) at above-solidus temperatures and at 1 GPa were obtained for a granite and amphibolite, which are considered to be major constituents of the continental crust. The temperature variation of velocities showed that the V_P values of granite decreased with rising temperature, but substantially increased beyond the melting temperature (850–900 °C). Such an increase may be caused by the α–β transition of quartz. The velocities of amphibolite decreased linearly with increasing temperature and dropped sharply at temperatures above the solidus (700 °C), indicating that partial melting of amphibolite acts to significantly lower the seismic velocities.  相似文献   

Extinction Behavior of Soil at 26.5 to 110 GHz     

Koh  G. 《Geoscience and Remote Sensing Letters, IEEE》2008,5(3):346-348

Soil electromagnetic properties at the microwave frequencies have been extensively documented in the literature. However, similar information at the higher millimeter frequencies is not available. A laboratory experiment was conducted to investigate the extinction behavior of wet and dry soil at millimeter wavelengths (26.5–110 GHz). For dry soil, the extinction coefficient increased from 0.02 to 0.6 $hbox{cm}^{-1}$ as the frequency increased from 26.5 to 110 GHz. The presence of even a small amount of water in the soil (5% by weight) reduced the penetration of millimeter wave signals into soil by a factor of ten.   相似文献   

Fe and Mn levels regulated by agricultural activities in alluvial groundwaters underneath a flooded paddy field     

Kangjoo Kim  Hyun-Jung Kim  Byoung-Young Choi  Seok-Hwi Kim  Ki-hoon Park  Eungyu Park  Dong-Chan Koh  Seong-Taek Yun 《Applied Geochemistry》2008

Iron and Mn concentrations in fresh groundwaters of alluvial aquifers are generally high in reducing conditions reflecting low SO₄ concentrations. The mass balance and isotopic approaches of this study demonstrate that reduction of SO₄, supplied from agricultural activities such as fertilization and irrigation, is important in lowering Fe and Mn levels in alluvial groundwaters underneath a paddy field. This study was performed to investigate the processes regulating Fe and Mn levels in groundwaters of a point bar area, which has been intensively used for flood cultivation. Four multilevel-groundwater samplers were installed to examine the relationship between geology and the vertical changes in water chemistry. The results show that Fe and Mn levels are regulated by the presence of NO₃ at shallow depths and by SO₄ reduction at the greater depths. Isotopic and mass balance analyses revealed that NO₃ and SO₄ in groundwater are mostly supplied from the paddy field, suggesting that the Fe-and Mn-rich zone of the study area is confined by the agricultural activities. For this reason, the geologic conditions controlling the infiltration of agrochemicals are also important for the occurrence of Fe/Mn-rich groundwaters in the paddy field area.  相似文献