On Pressure Pulse Techniques for Testing Low Permeability Geological Materials and Formations
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2Q3UHVVXUH3XOVH7HFKQLTXHVIRU 7HVWLQJ/RZ3HUPHDELOLW\*HRORJLFDO0DWHULDOVDQG)RUPDWLRQV M. Zhang* and M. Takeda* *Research Center for Deep Geological Environments, AIST, Tsukuba, Ibaraki 305-8567, JAPAN $%675$&7 The accurate hydraulic characterization of low permeability geological materials and formations has important practical implications, such as the geological disposal of radioactive nuclear waste. In this paper, we discuss pressure pulse techniques, which are methods that are commonly adopted both in the laboratory and LQVLWXfor testing low permeability geological materials and formations. The results obtained in this study illustrate that: 1) the use of nominal values for water compressibility will lead to significant underestimation of permeability from the pressure pulse tests; 2) specific storage is also an important parameter that should be evaluated simultaneously with permeability; 3) to shorten the time required to measure low permeability in the laboratory, it is advisable to use disk-shaped specimens; 4) when a geological formation is anisotropic, the value of permeability calculated using an isotropic model is between the maximum and minimum permeabilities of the geological formation; 5) the values of permeability and specific storage derived from an LQVLWXpressure pulse test may only reflect the hydraulic properties of the domain closely surrounding the test well. Caution should be exercised when interpreting data derived from the pressure pulse tests for the purpose of safety assessment. ,1752'8&7,21 There is international consensus concerning the geological disposal of radioactive nuclear waste in deep and stable geological formations. Through a system of multiple containment barriers, this strategy would isolate the waste from the biosphere for extremely long periods of time, and ensure that residual radioactive substances reaching the biosphere after many thousands of years would be at harmless levels. As a natural barrier to retard the migration of radionuclides accompanying underground flow of water, the most important feature of such geological formations should be low permeability. Although several methods are available for measuring the hydraulic properties of geological materials both in the laboratory [1] and LQVLWX[2], the pressure pulse techniques are commonly adopted because the times required for testing low permeabilities are much shorter than those required by other techniques. In this study, we discuss what factors may affect the results obtained by pressure pulse tests. The capabilities and accuracies of the pressure pulse techniques were examined because errors in permeability measurements could lead to significant misinterpretation of the suitability of a potential waste facility. 35(6685(38/6(7(&+1,48(6 &RQFHSWVDQGVROXWLRQV The laboratory pressure pulse technique was originally proposed by Brace HWDO [3]. This technique involves connecting the specimen ends to two fluid reservoirs, instantaneously increasing the fluid pressure in one reservoir, and mea
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