Applicability of the hydraulic conductivity determination of formation by pneumatic slug tests

To evaluate the permeability of a coastal formation in a seawater (saltwater) intrusion area and to introduce a method to select applicable slug test models, pneumatic slug tests were implemented using a Geoprobe system at different plane positions. Layered slug tests were also performed at several test sites. The matching-type curves method was used to calculate the hydraulic conductivity parameters of formation. The results show that, if the test target formation is a confined aquifer, good results are obtained from the calculations by analyzing either the overdamped oscillation slug tests using the KGS model or the underdamped oscillation slug tests using the Butler model. If the test target formation is an aquitard, the KGS model can be used to analyze the overdamped oscillation slug tests. The calculation results will be affected by the presence of an adjacent aquifer with high hydraulic conductivity and also by the inaccuracy associated with borehole logging. If the conditions of formation have unknown permeability grade, a reasonable slug test solution model must be chosen to calculate the hydraulic conductivity parameters precisely by analyzing concurrently the layer type, the formation type, the test well structure, and the characteristics of the water level recovery.