HR: 0800h
AN: NS31B-0377    [Abstracts]
TI: Heat-pulse flowmeter test to characterize the seawater intrusion in fractured rock, western coast of Korea
AU: * Oh, H
EM: ohayoun@yahoo.co.kr
AF: Hayoun Oh, 92, Gwahak-lo, Yuseong-gu, Daejon, 305-350, Korea, Republic of
AU: Hwang, S
EM: hwangse@kigam.re.kr
AF: Hayoun Oh, 92, Gwahak-lo, Yuseong-gu, Daejon, 305-350, Korea, Republic of
AU: Shin, J
EM: jehyun@kigam.re.kr
AU: Park, K
EM: kgpark@kigam.re.kr
AB: Seawater intrusion occurs commonly along the western and southern coasts of Korea. Almost coastal area consists of a reclaimed land, and is affected by seawater intrusion through the fractured rocks connected the seaside within several kilometers of coasts. A combination of drilling, conventional geophysical well logging including caliper log, natural gamma log, fluid temperature/conductivity log etc., acoustic televiewer, flowmeter, hydrophysical logging, packer test, and freshwater injection test was performed to evaluate seawater intrusion through the fractured rock in Baeksu-eup, Youngkwang-gun, Korea. The geological structure of the survey area comprises mud, sand, and granite and andesite bedrock (below an approximate depth of 22 m). The test boreholes are located with the brackish area interpreted with surface geophysical survey and hydrogeochemcial survey. The depth of two test boreholes is 50m, and the diameter is 3 inch, the distance between boreholes is 10m. Although the core log showed the several fractures, we didn't identify the minor fractures using 3-arm caliper logs because of small aperture size of fractures. The electrical conductivity of the borehole fluid is seen to be more than 1000 μS/cm at depth of about 35 m, and the highest conductivity is about 5000 μS/cm. Several intervals shown the change of conductivity logs doesn't relate with fractures identified by 3-arm caliper logs. In order to verify the permeable fractures, heat-pulse flowmeter test was conducted within single hole and interpreted with Paillet inversion method. Five permeable fractures are detected and hydraulic properties are estimated. These results are compared with hydrophysical logging performed one borehole. After the replacement of borehole fluid with freshwater, the change of fluid conductivity shows at least seven fractures with different salinity. Main fractures with highest salinity detected acoustic televiewer show low dip angles. To define subsurface connection between discrete fractures cross-borehole flowmeter test performed. To define subsurface connection between discrete fractures cross-borehole flowmeter test performed. Open flow path between two boreholes is detected at the depth of about 47 meters and this result agrees with freshwater injection test using double packer system. Open fracture at the depth of about 47 m didn't find with 3-arm caliper log, and all permeable fractures but only one below casing bottom are identified using acoustic televiewer log having almost low dip angles. In small-scale survey area the boundaries between andesite and granite intruded into andesite show impermeable fractures. Above results indicate that there are many flow paths with different salinity and depth through fractured rocks connected with seaside.
DE: 1835 Hydrogeophysics
SC: Near-Surface Geophysics [NS]
MN: 2007 Fall Meeting