Hydraulic borehole characterization through the application of moment methods to fluid conductivity logs

Abstract

In any type of groundwater transport problem (contaminant solutes, heat, etc.), knowledge of the location and properties of pathways of increased hydraulic conductivity is essential. However, answering such questions in strongly heterogeneous media, such as fractured rock, can be very difficult and budget-intensive with standard geophysical or hydrogeological field investigations. We present a new testing concept and analysis procedure based on a time sequence of wellbore electric conductivity logs, which provides the exact location and the outflow parameters (transmissivity, formation fluid conductivity) of flowing features (fractures, faults, layers) intercepted by the borehole. Previously the quantitative analysis of this time sequence of electrical conductivity logs was based on a code, called BORE, used to simulate borehole fluid conductivity profiles given these parameters. The present report describes a new direct (not iterative) method for analyzing a short time series of electric conductivity logs which is based on moment quantities of the individual outflow peaks, and applies it to synthetic as well as to field data. The results of the method are promising and are discussed in terms of the method's advantages and limitations. In particular it is shown that the method is capable of reproducing hydraulic properties derived from packer tests well within a factor of three, which is below the range of what is recognized as the accuracy of packer tests themselves. Furthermore the new method is much quicker than the previously used iterative fitting procedure and is even capable of handling transient fracture outflow conditions.