Borehole Flowmeter Application in Fluvial Sediments: Methodology, Results, and Assessment

Abstract

AbstractIn many situations, inadequate design or performance of ground‐water remediation systems is the result of underestimation of aquifer hydraulic heterogeneity, and in particular, the vertical variation of hydraulic conductivity which plays an important role in contaminant migration. Described herein are applications of the electromagnetic (EM) borehole flowmeter to fluvial sediments in Louisiana and South Carolina. The direction of natural vertical flow in the test aquifers was defined easily, and short pumping tests enabled the calculation of hydraulic conductivity profiles for each test well. The results correlated well with other information obtained independently, including natural gamma logs, driller's logs and a hydraulic conductivity profile based on grain size analysis. Large variations in hydraulic conductivity over short vertical and horizontal distances were documented. Tests in gravel‐packed wells suggested that flowmeters produce misleading data for a variety of reasons in such situations. Among other things, an annulus of high permeability around a well screen allows flow to bypass the meter, and the phenomenon is amplified by high pumping rates. The resulting error is displayed as an erroneous high permeability zone at the top of the well screen. This observation deserves further study. In its present form the EM flowmeter is awkward to handle on a routine basis. However, none of the present design flaws preclude its effective use.