FIELD EVALUATION OF A NEW BOREHOLE RESISTIVITY PROBE USING CAPACITIVE ELECTRODES.

A prototype resistivity probe using capacitive electrodes has been built under a collaborative project funded jointly by the Geological Survey of Canada (GSC) and IFG Corporation, a Canadian manufacturer of borehole geophysical instrumentation. The GSC carried out field tests at its borehole test facilities in Ottawa and at the New Calumet massive sulphide deposit in Quebec. Results indicate that the capacitive technique is sensitive in the resistivity range 10010,000 ohm-m and compares well with galvanically and inductively measured resistivities. Field tests were also carried out for several transmitter-receiver spacings and in plastic-cased fluidfilled boreholes. Capacitive resistivity logs acquired in a plastic-cased borehole are almost identical to those acquired in the same but uncased borehole. Therefore, capacitive resistivity logs promise to be valuable for use in environmental applications where boreholes drilled in unconsolidated sediments are often plastic-cased.