HR: 0800h
AN: H21C-1358    [Abstracts]
TI: Numerical Examination of the Effective Investigation Areas by Single-Well Hydraulic Tests in Low-Permeability Environments
AU: * Takeda, M
EM: mikio-takeda@aist.go.jp
AF: Research Center of Deep Geological Environments, National Institute of Advanced Industrial Science and Technology (AIST), Central 7, 1-1-1, Higashi, Tsukuba, 305-8567 Japan
AU: Zhang, M
EM: m.zhang@aist.go.jp
AF: Research Center of Deep Geological Environments, National Institute of Advanced Industrial Science and Technology (AIST), Central 7, 1-1-1, Higashi, Tsukuba, 305-8567 Japan
AU: Nakajima, H
EM: nakajima.hideo@aist.go.jp
AF: Research Center of Deep Geological Environments, National Institute of Advanced Industrial Science and Technology (AIST), Central 7, 1-1-1, Higashi, Tsukuba, 305-8567 Japan
AB: In-situ permeability tests are indispensable for hydraulic characterizations of investigate areas for the geological disposal of radioactive nuclear waste. The single-well permeability tests are preferable in the course of site selection, and the derived hydraulic parameters are important indices of the capabilities of a candidate site to retard nuclide migration and the parameters required for the subsequent prediction of nuclide fate based on transport modeling. However, the hydraulic parameters obtained from any in-situ permeability test may only reflect the hydraulic characteristics of the area around the well that has experienced a pressure disturbance due to the test. Since the area influenced during a test depends on the test time, hydraulic characteristics and their distributions in the formation, and the test method itself, the parameters derived from a test data may vary between tests. Accordingly, application of a test result should also consider the effective investigation area of each test method. To examine the effective investigation areas for different types of single-well permeability test in low permeability environments, numerical simulations for the major test methods, i.e., the pressure pulse test, constant head test, constant rate test, were performed in this study. Pressure responses around the test well, the variations of measurement data and hydraulic gradients around the well were also calculated to assess the behavior of each test method. A series of numerical examinations yielded the following findings: (1)In the constant head and constant rate tests, the influenced areas expand and their response values reach the same values of a constant head and constant flow rate at the well as time elapses. On the other hand, the influenced area in the pulse test is very limited and the induced hydraulic head diminishes within that area. (2)The times required for individual tests to establish the quasi-steady state are almost the same. The duration of transient state in each test method depends on the hydraulic properties of formation and tends to increase in low-permeability environments. (3) The hydraulic gradients around the well reach their maximum values early in the pressure pulse and constant head tests and decrease with time. On the other hand, the hydraulic gradient gradually increases from the vicinity of the well screen with time in the constant rate test.
DE: 1805 Computational hydrology
DE: 1829 Groundwater hydrology
DE: 1849 Numerical approximations and analysis
DE: 1859 Rocks: physical properties
DE: 1894 Instruments and techniques: modeling
SC: Hydrology [H]
MN: Fall Meeting 2005