The analysis of slug tests in the frequency domain.

In this paper a generalized analytical frequency domain method for the evaluation of transmissivity tests is presented. For a confined homogeneous aquifer the Kelvin functions represent a satisfactory set of solutions for the equation of radial flow in the frequency domain. Depending on the type of transmissivity test, simple analytical frequency-dependent transfer functions can be defined, which relate the reaction of the aquifer to any pressure disturbance. Hence a numerical Fourier transform of the field data can be performed to determine a transfer function of data, which can be fitted with the analytical one. In order to estimate the hydraulic parameters a special logarithmic Fourier transform was used to analyze synthetic data of a slug test to verify this approach. The consideration of transmissivity tests in the frequency domain leads to some promising prospects. With this method a radius of penetration for each excitation frequency can be defined. Furthermore, analytical solutions for radial symmetric permeability distributions are available (e.g., consideration of a gravel pack or a developed zone). The frequency domain approach is also extended to a new type of low-cost transmissivity test, the hydraulic impedance test. [ABSTRACT FROM AUTHOR]