Theoretical Model and Experimental Research on Determining Aquifer Permeability Coefficients by Slug Test under the Influence of Positive Well-Skin Effect

Abstract

In the process of slug test in the field, mud and debris may infiltrate into the aquifer during the formation of the test well, and a poorly permeable annulus area appears around the test well wall. This is called the positive well-skin effect, which can have a significant impact on the results of slug tests due to the characteristics of a slug test. Therefore, to carry out the research on the determination of aquifer permeability coefficients by slug test under the influence of positive well-skin effect, a mathematical model of a slug test considering the positive well-skin effect was constructed. The Laplace transform method and the AWG algorithm were used to solve for a series of standard curves, and specific steps were given for calculating aquifer permeability coefficients by slug test under the influence of positive well-skin effect. Meanwhile, an indoor test model with positive well-skin effect was constructed, then several sets of slug tests and pumping tests with different excitation strengths were carried out. Based on this study, the presence of positive well-skin layer had a great impact on the aquifer permeability coefficient determined from both the pumping test and Kipp model of slug test, resulting in smaller results. The HWS model overcomes the influence of positive well-skin effect. This will further improve the theory of slug test, increase the accuracy of slug test in determining the permeability coefficient, and promote the application scope of slug test. It is therefore possible to discern the well-skin factor and determine the aquifer permeability coefficient by fitting the slug test data to a standard curve.