Determination of Fracture Inflow Parameters With a Borehole Fluid Conductivity Logging Method

There is much current interest in determining the flow characteristics of fractures intersecting a well bore in order to provide data for use in estimating the hydrologic behavior of fractured rocks. Inflow rates from these fractures into the well bore are usually very low. Moreover, in most cases only a few percent of the fractures identified by core inspection and geophysical logging actually conduct water, the rest being closed, clogged, or isolated from the water flow system. A new procedure is proposed and a corresponding method of analysis developed to locate water-conducting fractures and obtain fracture inflow rates by means of a time sequence of electric conductivity logs of the borehole fluid. The physical basis of the analysis method is discussed, and 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. By applying our analysis to these nine peaks, the flow rates and the salinity of the water from these fractures are determined. These results are used with other information to obtain transmissivities of the nine fractures, which are validated against independent hydraulic measurements by packer tests. The salinities measured in fluids from the fractures are also validated against salinity values obtained by chemical sampling of fluids from different depths of the borehole. The applicability of this technique is discussed in the context of a borehole-testing program.