The Bells Corner borehole geophysical calibration facility of the Geological Survey of Canada

Abstract

Calibration sites provide important opportunities for the standardization of downhole instrument response. Using quantitative physical properties from borehole cores, calibration adds value to projects by allowing for data consistency from hole-to-hole, system-to-system, and importantly, over time. The Geological Survey of Canada (GSC) maintains the Bells Corners Calibration Facilities near Ottawa, Canada, which is available to all members of the geophysical logging community. In the late 1970's and early 1980's, the GSC developed quantitative borehole calibration facilities, consisting of model calibration boreholes for gamma-ray spectral logging probes with known concentrations of potassium (K), uranium (U), and thorium (Th), density calibration blocks for gamma-gamma tools, and six deep boreholes in Palaeozoic sedimentary (sandstone, dolomite, shale) and Precambrian (granitic) bedrock. The deep boreholes were continuously cored, range in depth from 120 - 300 m, and are sited within a 10 to 100 m triangular configuration for cross-hole capabilities. The published downhole log suite includes spectral gamma-ray, density, neutron, induced polarization (IP), self potential (SP), resistivity, acoustic velocity, magnetic susceptibility, and fluid temperature. In recent years, new GSC calibration datasets have been collected in these wells including high-resolution televiewer imaging, acoustic velocities, and high-resolution temperature and fluid conductivity. An effort is underway to update downhole and petrophysical core measurements, maintain standardization for traditional downhole instruments, and conduct demonstration projects with newly developed downhole instruments so that sites remain relevant to members of the groundwater, geotechnical, and extractive sectors.