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Shape factors for constant‐head double‐packer permeameters
Author(s) -
Mathias S. A.,
Butler A. P.
Publication year - 2007
Publication title -
water resources research
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.863
H-Index - 217
eISSN - 1944-7973
pISSN - 0043-1397
DOI - 10.1029/2006wr005279
Subject(s) - permeameter , hydraulic conductivity , hydraulic head , head (geology) , shape factor , constant (computer programming) , mathematics , hydraulics , geotechnical engineering , equipotential , mechanics , geometry , conductivity , flow (mathematics) , geology , mathematical analysis , soil science , engineering , physics , thermodynamics , computer science , quantum mechanics , geomorphology , soil water , programming language , electrical engineering
Local estimates of hydraulic conductivity are often obtained from constant‐head double‐packer tests. The tests yield ratios of flow against head difference. These are converted to values of hydraulic conductivity by dividing by a shape factor. Previously used shape factors have generally assumed that the packers are infinitely large. Such shape factors lead to overestimates of hydraulic conductivity as they ignore the effect of water flow around the packers. A semianalytical solution is derived for a constant‐head double‐packer permeameter test. The solution is compared with existing, approximate techniques, including the spheroidal equipotential solution, the narrow packer approximation of Rehbinder (1996), and the long‐packer approximation of Rehbinder (2005). Generally, it is shown that ignoring the length of the packer and assuming a fully cased well lead to an overestimate of hydraulic conductivity. The significance of this reduces with increasing well‐screen aspect ratio. Evaluation of the solution is nontrivial. For this reason, a polynomial relationship between shape factor, well‐screen aspect ratio, and packer length (obtained by curve fitting with the semianalytical solution) is provided.