The applicability of slug tests in fractured-rock formations

Abstract

Currently slug tests in South Africa are used with two objectives in mind: • To get a first estimate of the yield of a borehole. • To estimate the K-value (or T-value) of the aquifer near the borehole. The paper shows that the use of currently available slug-test interpretation methods to analyse slug tests in fractured-rock aquifers to estimate a T or K-value is problematic. The estimated value is dependent on the flow thickness (thickness of the part of the aquifer in which flow occurs due to the slug input). If this thickness of flow is known, the estimated T-value is more representative of that of the fracture zone. By using the total thickness of the formation for the estimation of the K-value in slug-test analysis, the estimated K-value (and thus KD-value) does not represent the T-value of the formation.