The Physical Reasons to Have Underdamped or Oscillating Variable-Head (Slug) Tests: A Review and a Clarification

What is it about?

Variable-head permeability or slug tests may yield an oscillating water level in the riser pipe, or UD response. It is found that all UD solutions are incomplete because they solve one half of the problem – for the water in the pipe – and ignore the second half, seepage in the tested material. These half-solutions violate mathematical rules for the second half and thus, are incorrect. Four reasons for oscillations are examined. The major finding is that a free space along the casing or some trapped gas is needed to observe large oscillations. Hence, an oscillating response only proves that the MW or a packer is poorly installed. This MW yields wrong values for hydraulic head, gradient and water analyses.

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