Lawrence Berkeley National Laboratory

The flowing fluid electric conductivity (FFEC) logging method is an efficient way to provide information on the depths, salinities, and transmissivities of individual conductive features intercepted by a borehole, without the use of specialized probes. Using it in a multiple-flow-rate mode allows, in addition, an estimate of the inherent "far-field" pressure heads in each of the conductive features. The multi-rate method was successfully applied to a 500-m borehole in a granitic formation and reported recently. The present paper presents the application of the method to two zones within a 1000-m borehole in sedimentary rock, which produced, for each zone, three sets of logs at different pumping rates, each set measured over a period of about one day. The data sets involve a number of complications, such as variable well diameter, free water table decline in the well, and effects of drilling mud. To analyze data from this borehole, we apply various techniques that have been developed for analyzing FFEC logs: direct-fitting, mass-integral, and the multi-rate method mentioned above. In spite of complications associated with the tests, analysis of the data is able to identify 44 hydraulically conducting fractures distributed over the depth interval 150-775 meters below ground surface. The salinities (in FEC), and transmissivities and pressure heads (in dimensionless form) of these 44 features are obtained and found to vary significantly among one another. These results are compared with data from eight packer tests with packer intervals of 10-80 m, which were conducted in this borehole over the same depth interval. They are found to be consistent with these independent packer-test data, thus demonstrating the robustness of the FFEC logging method under non-ideal conditions.