Quantifying the Effects of Well Development in Unconsolidated Material |
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| Authors: | Gilles Wendling Robert P Chapuis Denis E Gill |
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| Institution: | École Polytechnique, Department of Mineral Engineering, P.O. Box 6079, Sta. Centre-ville, Montréal, Québec, Canada, H3C 3A7.;Presently, Morrow Environmental Consultants, 8658 Commerce Court, Burnaby, B.C., Canada, V5A 4N6. |
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| Abstract: | A fully instrumented physical model was designed and built to reproduce development by surging and monitor its effects during surging and after development. The model simulates a horizontal layer in a confined aquifer with control of vertical overburden pressure. An automatic apparatus produced development by surging in successive phases up to 24 hours. Aquifer tests in steady-state conditions were performed between successive phases. The paper reports the main results of three experiments performed with Johnson screens 200 mm in diameter; they had slot sizes between the D54 and D70 of the aquifer soil. This soil was placed under controlled conditions, and initial homogeneity was obtained as confirmed by initial control tests. Pore pressures (and thus hydraulic heads) were continuously monitored during development phases and aquifer tests by 22 electronic piezometers at distances between 0 and 1 m from the screen. These piezometers measured water pressures every 0.1 s when required. Solid particles passing through the screen were recovered to study the solid yield and the gradation of particles. Positive and negative values of local gradients reached values up to 400 close to the screen at the beginning of development and decreased with time of development. These high values produced high seepage forces displacing particles in the aquifer. The well yield was increased by a factor of 6 after development. These model test results confirmed empirical criteria on entrance velocity, internal stability criteria, and field values of "sand" production by development. In addition, they enabled a quantification of skin effects to be considered in interpreting an aquifer test. |
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