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TitleBorehole geophysical calibration facilities of the Geological Survey of Canada in Ottawa, Canada
AuthorCrow, H; Cartwright, T; Brewer, K; Pugin, A J -M
Alt SeriesNatural Resources Canada, Contribution Series 20180213
PublisherEnvironmental and Engineering Geophysical Society
Documentserial
Lang.English
Mediaon-line; digital
ProgramAquifer Assessment & support to mapping, Groundwater Geoscience
Abstract(unpublished)
Calibration sites provide important opportunities for the standardization of downhole instrument response. Using quantitative physical properties from bedrock cores and constructed model boreholes, 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 a facility for calibrating and testing borehole geophysical instruments and downhole gamma-ray spectrometers near Ottawa, Canada, which is open to all members of the logging community.
The facility, developed by the GSC to international standards in the late 1970's and early 1980's, consists of two parts (Figure 1). The first site is a series of six deep test boreholes drilled in Palaeozoic sedimentary (sandstone, dolomite) and Precambrian (granite, gneiss) bedrock (Figure 2). The boreholes are 76 mm in diameter (NQ) and intersect numerous geological formations and structures with varied physical properties. The boreholes were continuously cored, range in depth from 120 - 300 m, and were sited within a 10 m to 100 m triangular configuration for cross-hole capabilities. A series of published logs allow for the calibration of resistivity, induced polarization, sonic velocities, density, spectral gamma, magnetic susceptibility, and borehole fluid properties (Bernius, 1996). The boreholes have been used for many decades by government and industry to test and evaluate new instruments and logging methodologies.
The second site consists of a series of nine model calibration columns for spectral gamma-ray logging probes (Figure 3). The concrete-encased boreholes contain intervals of known concentrations of potassium (ranging from 0.80 -3.28%), uranium (16 - 998 ppm), and thorium (11 - 504 ppm) which allow for the calculation of calibration factors relating a tool's measured count rate to a known ore concentration. Each column contains three borehole diameters (AQ=48 mm, BQ=60 mm, NQ=76 mm) which can be logged dry or wet, depending on the borehole conditions to be encountered in the field. Details of the facility can be found in Mwenifumbo et al. (2005).
The facility marked its 40th anniversary in 2017 and continues to be visited by members of industry and government. Work is ongoing to maintain the facility, such as the refurbishment of the deck above the calibration columns, and inspections of bedrock borehole conditions. Importantly, over the coming few years, an effort is underway to update petrophysical core measurements, maintain standardization for traditional instruments, and conduct logging with newly developed downhole instruments so that facilities remain relevant to members of the mineral exploration, groundwater, and geotechnical sectors. Information (detailed site description, logs) can be downloaded through the GSC's Geoscan website (Open File 3157 and 4383). Currently, site access can be arranged by contacting the GSC (Tim Cartwright, Tim.Cartwright@canada.ca, or Heather Crow, heather.crow@canada.ca).
Summary(Plain Language Summary, not published)
Calibration sites provide important opportunities for the standardization of downhole instrument response. Using quantitative physical properties from bedrock cores and constructed model boreholes, 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 maintains a facility for calibrating and testing borehole geophysical instruments and downhole gamma-ray spectrometers near Ottawa, Canada, which is open to all members of the logging community. This news article for FastTIMES, an electronic newsmagazine for the near-surface geophysical sciences, describes the facility and efforts to maintain the site for ongoing calibration and research initiatives.
GEOSCAN ID311285