Establishment of Laboratory Hydraulic Tests for Saturated and Unsaturated Low-permeability Rocks

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We clarified some major problems in using conventional laboratory methods for testing low permeability geological materials. A new and versatile laboratory system is devised that can implement any of the three test methods, the constant-head, flow-pump and transient-pulse tests, while maintaining relatively low hydraulic gradients and subjecting a specimen to high confining pressures and pore pressures, thereby simulating in situ conditions at great depths. To exam the capabilities of this new laboratory system, a series of cross-check permeability tests is also performed on Shirahama sandstone and Inada granite. The major conclusions drawn from this research are as follows:(1) The permeabilities derived from the three complementary laboratory methods are in general agreement with variations in the same order. These differences may reflect the errors arising from measuring substantial changes in hydraulic pressure at very early times during the pulse test. They may also be related to v … More ery small plumbing leaks or slight temperature variations that affect long-term test response.(2) The test durations for the constant-head and the constant flow-rate tests are roughly the same and so are the resulting permeability values. Since a "real" or "reference" value for permeability is unknown, we cannot assess which technique is the best. However, further comparison among techniques and examination of the results does increase the accuracy of testing low-permeability specimen and achieve consistent results.(3) The rigorous theoretical analysis of the transient-phase data obtained during a constant flow-rate test permits the test duration to be significantly shortened without sacrificing accuracy in estimating both the permeability and the specific storage of a test specimen.(4) According to the ASTM standards (D5084), it is recommended to use hydraulic gradient less than 30 when testing specimens having very low hydraulic conductivities (less than about 1 x 10-9m/s). A series of cross-check permeability tests were successfully performed under this conditions. Less