A Model to Simulate Pumping Tests in Wells with High Loss and Backflow |
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| Authors: | M Wojciech Kawecki |
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| Institution: | 1. Groundwater Division, Saudi Aramco, Dhahran 31311, Saudi Arabia;2. +966 3 872 8441;3. fax: +966 3 872 9379;4. kaweckmw@aramco.com |
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| Abstract: | Traditional methods of analyzing pumping tests in single wells fail when the well loss is very high due to a low transmissivity skin. Because of the restricted rate at which water can enter a high loss well from the aquifer, well casing storage becomes a significant factor. Additionally, if a slug of water enters the well from the pump column immediately after the pump is switched off, it has a long‐lasting significant effect on the recovering water level in the well because it cannot be absorbed rapidly by the aquifer. A theoretical model is derived here that simulates the water level in a well in these circumstances. In the model, the continuously changing rate of water inflow from the aquifer to the well is approximated by a step function with a finite difference time step. It is demonstrated by a real example that the model can be applied easily to analyze pumping tests, including tests with a varying pumping rate. The analysis confirms suspected high well loss, calculates the unknown rate of backflow, and determines the aquifer's transmissivity. |
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