Transient Hydraulic Tests in Granite: Fissured Porous Medium Analysis and Results
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Stephen V. Topp,
Science Publishing Company, by Elsevier BASIS FOR NUCLEAR WASTE MANAGEMENT
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223
editor
TRANSIENT HYDRAULIC TESTS IN GRANITE: FISSURED POROUS MEDIUM ANALYSIS AND RESULTS
JOHN H. BLACK AND JOHN A. BARKER* Institute of Geological Sciences, Harwell Laboratory,
Oxfordshire,
England
ABSTRACT Slug and pulse tests have been used extensively to measure the hydraulic conductivity and specific storage of After several hundred tests using an I.G.S. granitic rocks. design of straddle packer test equipment, it became clear that the conventional methods of test analysis were The straddle packer equipment developed by IGS inadequate. allows the time scale of a test to be altered without repositioning the packers so that a range of tests can be The new analysis carried out on the same test interval. procedure presented here uses a model of fissured rock which incorporates water movement in both the fissures and the rock A new variable is introduced which includes the matrix. parameters matrix hydraulic conductivity, matrix specific storage fissure specific storage and fissure hydraulic conductivity together with the controllable variables, Examples effective casing radius and packer interval length. of analysis using multiple tests in the same interval are presented together with the apparent relationship between It measured hydraulic conductivity and specific storage. would appear that a small number of fissures endow the rock mass with the bulk of its hydraulic conductivity and that many of the higher hydraulic conductivity tests are probably associated with localised "pipe flow".
INTRODUCTION A large number of transient hydraulic tests in crystalline rock have been carried out by the Institute of Geological Sciences (IGS) within the U.K. programme on the feasibility of the disposal of high-level radioactive waste to geological formations. A test site at Altnabreac in northern Scotland was half of 1979 and since then the hydraulic properties of drilled during the first the rocks immediately surrounding three 300 m deep boreholes have been measured. A wireline straddle packer system [1] was designed to allow water to be abThe constraint was stracted from (rather than injected into) the test section. imposed because the boreholes are used as sampling points for the measurement of A feature of the system is that it allows variation of groundwater chemistry. the amount of water required to flow into the test section for a given reduction Thus it is possible to carry out both pulse tests of test section pressure [1]. [2) and slug tests [3,4] on the same test section without moving the packers. Both tests involve a sudden change in test section pressure which is followed by a diagnostic period of pressure equalisation resulting from flow of water into For the slug test the equalisation depends on the or out of the section. movement of a water level in an open tube (usually the casing of the borehole *Institute of Geological Sciences, Oxfordshire, England.
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