Technical Report NTB 88-13

It is of much current interest to determine the flow characteristics of fractures intersecting a wellbore in order to provide data in the estimation of the hydrologic behaviour of fractured rocks. In particular the fluid inflow rates from the fractures into the wellbore are important quantities to measure. However often these inflows are at very low rates. In addition very often one finds that only a few percent of the fractures identified by core inspection and geophysical logging are water-conducting fractures, the rest being closed, clogged or isolated from the water flow system. A new developed to locate water-conducting fractures and obtain fracture inflow parameters by means of a time sequence of electric conductivity logs of the borehole fluid. The physical basis of the analysis method is discussed. The procedure is applied to an existing set of data, which shows initiation and growth of nine conductivity peaks in a 900 m section of a 1690 m borehole, corresponding to nine water-conducting fractures intersecting the borehole. We are able to match all nine peaks and determine the flow rates from these fractures. A discussion is given on the applicability of this technique in the context of a borehole testing program.