Improved Estimates of Hydraulic Conductivity and Specific Storage from Straddle Packer Tests in Fractured Sandstone

Tuesday, September 24, 2013: 1:50 p.m.
Pat Quinn , School of Engineering, University of Guelph Guelph, Guelph, ON, Canada

A method is presented for obtaining depth-discrete values of specific storage (Ss) for short test intervals in single boreholes in fractured rock. The test equipment, described by Quinn et al. (2012), is used to conduct four types of hydraulic tests in each test interval: constant head step tests, slug tests, and pumping/recovery tests. Hydraulic conductivity (K) values are obtained from the constant head step test and slug tests, avoiding errors due to non-Darcian flow. The pumping tests, which have a duration of one half to two hours, provide values for hydraulic diffusivity (K/Ss) obtained by the standard Theis-based curve fitting method. To minimize the usual uncertainty in the hydraulic diffusivity values inherent in the curve fitting methods, the Darcian K values obtained from the constant head step test and slug tests are used to constrain K in the curve fitting procedure to obtain the best value for specific storage (Ss). Care is taken to account for wellbore storage, most influential during the first few minutes of pumping tests and to avoid boundary effects that may influence late-time results. This procedure was applied in 1.5 m intervals in boreholes between 200 and 800 ft deep in a sandstone aquifer which has high fracture density and rock matrix porosity of 5-15%. In this study K values of the sandstone ranged from 3.8 to 7.5 × 10-5 m/s and the Ss values were on the order of 10-6-10-5 m-1, consistent with values reported in the literature. Improved estimates of K and Ss provide much more insight into the hydraulic properties of the fracture network, and allow improved calculation of hydraulic apertures and effective fracture porosities for estimating average linear groundwater velocities. This study illustrates the benefits of conducting four different types of hydraulic tests to gain confidence in both K and Ss.

Pat Quinn, School of Engineering, University of Guelph Guelph, Guelph, ON, Canada
Patryk Quinn completed a Ph.D. in Contaminant Hydrogeology at the University of Waterloo under the supervision of Beth Parker and John Cherry in September 2009, and is currently working as a research scientist in the School of Engineering at the University of Guelph in the G360 research group focusing on hydraulic testing in fractured rock environments.


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